Your San Francisco startup glued together six SaaS tools and now the seams are the product
Custom software for a San Francisco tech company runs $90k to $280k and takes 5 to 10 months. You build instead of assembling off-the-shelf SaaS when your core workflow is your differentiation, the integration glue between tools has become its own fragile system, or generic SaaS forces your users into a process that contradicts how your product is supposed to work. Most early-stage San Francisco startups should buy and glue until the glue itself becomes the thing customers complain about.
You moved fast by buying everything: a SaaS for workflows, another for data collection, a third for notifications, a fourth for analytics, all wired together with Zapier and a couple of cron jobs. It got you to product-market signal. Now the glue is the system. A change in one vendor's API breaks two downstream automations, your data lives in six places that disagree, and the experience your customers see is stitched from tools that were never meant to know about each other. Your San Francisco product's roadmap is now hostage to other companies' release schedules.
Generic off-the-shelf SaaS is the right call when your process looks like everyone else's. It becomes a ceiling the moment your differentiation lives in a workflow no vendor sells. An AI company whose value is a specific human-in-the-loop review process, a fintech whose edge is a particular underwriting flow, a biotech whose lab data pipeline is unlike anyone else's, none of them can buy their core. The 80% a SaaS covers is the commodity part; the 20% it can't is exactly where your company is supposed to win.
Budgeting a custom software build in San Francisco
| Project scope | Typical cost | Timeline |
|---|---|---|
| MVP: core workflow engine + data model | $90k to $150k | 4 to 6 months |
| Full platform replacing the SaaS glue | $180k to $280k | 8 to 10 months |
| Integration layer + selective SaaS replacement | $70k to $130k | 3 to 6 months |
The case for owning your custom software
You build custom when the workflow is the moat. A San Francisco startup's defensibility usually lives in a process, an AI-assisted review loop, a novel underwriting model, a lab-to-analysis pipeline, that no off-the-shelf SaaS was built to run. Custom software lets you own that core workflow end to end, control its data model, and ship improvements on your timeline instead of a vendor's. Once the integration glue between rented tools costs more engineering time than the features customers ask for, building the core yourself stops being a luxury.
- Your differentiating workflow can't be bought and the SaaS workarounds contradict how your product should work
- Integration glue between rented tools breaks regularly and consumes more engineering than new features
- Your data disagreeing across six tools is causing reporting errors and customer-facing mistakes
- Your roadmap is repeatedly blocked on a vendor's release schedule you can't influence
- Your process is genuinely standard and a SaaS covers it well
- You're pre-product-market-fit and still discovering what the workflow even is
- The part you'd build is a commodity like auth, billing, or email
- You lack the engineering bandwidth to maintain custom software long-term
What your build should include
What we build under custom software in San Francisco
Everything a custom software build here can cover: API development, cloud software, MVP development, legacy modernization, systems integration and microservices.
Delivery, week by week
Exactly what you get
An owned core where your differentiation lives: a purpose-built engine for the workflow no SaaS sells, on a single coherent data model that ends the reconciliation tax, with clean APIs to the commodity tools you smartly keep buying. For an AI company that means a logged, improvable human-in-the-loop layer; for a fintech, your actual underwriting flow as first-class software. You get observability and audit logging built in for security reviews, and integration with your custom CRM, ERP, and business intelligence dashboards so the whole stack finally tells one story.
How to choose a developer in San Francisco
San Francisco engineering leaders respect teams that know what not to build, so hire the agency that argues with your scope. A strong partner will identify your differentiating 20% and tell you to keep renting the commodity 80%, rather than quoting a from-scratch rebuild of auth and billing. Ask how they'd consolidate six disagreeing data sources into one model without losing history, and how they design for a security review from day one. Insist on a paid discovery that inventories your current SaaS glue before anyone commits to a build.
- You own your core workflow end to end, so improving it is a sprint instead of a vendor support ticket
- One coherent data model instead of six SaaS tools that disagree and need constant reconciliation
- Your roadmap stops being hostage to other companies' API changes and release schedules
- The experience customers see is designed, not stitched, which matters in a market that judges polish in seconds
- Defensibility: competitors can buy the same SaaS stack you abandoned, but they can't buy your custom core
- You replace a predictable subscription with a build cost and a permanent maintenance commitment
- Building badly is worse than buying; a weak team ships fragile custom software harder to fix than the SaaS it replaced
- Commodity parts (auth, billing, email) should still be bought; rebuilding them is wasted money and risk
- Custom software needs ongoing engineering forever, which competes with the customer-facing roadmap
- !They want to rebuild everything including commodity auth and billing; ask what they'd keep buying
- !No questions about which workflow is your actual differentiation; ask them to identify your 20%
- !They skip the data migration plan; ask how six disagreeing sources become one model without losing history
- !They've never built an AI-in-the-loop system; ask for a reference if that's your core
- !They quote a fixed price before mapping your current stack; ask them to inventory the glue first
Most San Francisco teams pricing custom software end up comparing notes on website, inventory management, warehouse management too; the systems share one data spine.
Rohan advises mid-market and enterprise teams on ERP, CRM and custom software, and has led delivery on dozens of business-software builds.
Writes for Digital Heroes, shipping business software for 2,000+ brands across 55+ countries since 2017.
Frequently asked questions
Should a San Francisco startup build custom software or assemble SaaS?
Assemble SaaS until the integration glue becomes its own fragile system or your differentiating workflow can't be bought. The trigger is usually vendor API changes breaking your product plus a core process that generic tools actively contradict.
How much does custom software development cost in San Francisco?
A core workflow engine and data model MVP runs $90k to $150k. A full platform replacing your SaaS glue runs $180k to $280k over 8 to 10 months. A selective integration-plus-replacement project runs $70k to $130k.
Can we keep some SaaS tools and build only the core?
Yes, and you should. The right approach builds your differentiating workflow custom while continuing to buy commodity pieces like auth, billing, and email, connected through clean APIs instead of fragile Zapier chains.
What workflow justifies custom software for an AI company?
Usually a human-in-the-loop review process where model output and human judgment both need to be first-class, logged, and continuously improvable. That loop is your defensibility and no off-the-shelf SaaS is built to run it.