The comparison that matters is a per-seat recurring fee against hosting, maintenance, monitoring, backups and one accountable person. Open source usually wins on a growing headcount and a process specific to your business. It loses when a small team has nobody to operate infrastructure.
A vendor who tells you one side always wins is making a sales argument.
What do you actually pay on each side?
With SaaS you pay a licence that scales with seats, contacts, events or tasks, and the vendor absorbs hosting, patching and uptime. With open source you pay for a server, for the engineering to deploy it properly, and for the attention a running system keeps demanding.
The break-even is arithmetic. Multiply the subscription by the seats you expect in 24 months, add the migration cost you would face if the price became unacceptable, then compare that total to a one-time build plus the honest operating line.
What costs are forgotten on the open-source side?
Backups somebody has actually restored. A cadence for updates and security patches. Upgrade rehearsals before a version jump breaks an integration. Monitoring that tells you about a failure before a customer does. And a named person who knows how the thing is put together, which is the item most often missing and the one that decides whether self-hosting was a good idea.
Add those up before you decide. A stack that costs nothing per seat can still be the expensive option if it eats a person's attention.
What costs are forgotten on the SaaS side?
Per-unit growth you did not model. Renewal increases that arrive with no negotiation leverage. Integration limits that reshape your process around the product. A data export without the joins you need. Switching costs high enough to make all of that acceptable for one more year.
Price the subscription over the period you intend to keep it, and those stop arriving as surprises.
Where is open source the wrong answer?
When a regulator or a client contract requires a certified vendor. When the open-source option in a category is immature and you would end up maintaining it yourself. When nobody in the company wants to be responsible for a server. When your volumes are low enough that the subscription costs less than hosting and attention.
All four are common, and saying so is part of the work. See when you should not self-host.
How do you run this comparison for your own stack?
List each tool, what it does, what it costs per year and who depends on it. Mark the load-bearing ones, the systems your revenue runs through, and leave the conveniences alone. Load-bearing systems with a mature open-source equivalent are the ones worth owning.
Price the migration for those and nothing else. The whole analysis takes an afternoon with your invoices, before any vendor gets involved.
Name one process that still needs a person. We will tell you what a one-time build takes.
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