to me that translates as "WARNING! TRAP!" because I may decide I like your thing, and then my users may decide they like _my_ thing, and then suddenly I find out what your price is for my scale and "oh shit! I'm going to go broke OR have to recode everything"

ESPECIALLY since this would become a key part of the infrastructure / how my app gets its stuff done. Replacing your service with a competitor or something homebrew would be a major pain, especially when I find myself unexpectedly popular.

there is NO WAY I would ever use or recommend a service that refuses to tell me what my potential long term costs are up front.

It's too much of a gamble with a business or worse, a hobby project that isn't making me any money to compensate for this unexpected "balloon payment".

Kind of agree with this. As a business you want to have not only your present costs, but your future costs known. No surprises.

RMS has the solution here: “Free” software. If they shut down you have the source and can self host on aws.

The OP was asking what the price is when they do have an enterprise use case or their scale grows beyond your defined constraints.

Most vendors that aim for enterprise contracts take a "contact us" approach. Contracts can be negotiated. Pricing may vary.

(I am not affiliated with this vendor, I just deal with software vendors a fair bit.)

Vendors that are aiming at a split workflow, with a free tier and a paid tier usually have some set paid tiers and then a “contact us” for beyond that. For example, Slack gives you prices for the Standard and Support plans, and then lets enterprises contact them for negotiating prices. The problem with Pipedream is that non-enterprise customers will want to use their so-called enterprise plan.