For testing one could use any other webkit browser. Most of them have similar rendering quirks to Safari.

They still have webkit builds for Windows and Linux etc, and you still don't need to buy anything special to run it. I think they also have a (mostly?) headless one, and a mini-browser which is intended to test the engine (so it doesn't have things like bookmarks or profiles or anything like that, a good fit). Similar options exist for FireFox and Chromium so it's not really a Safari/Webkit special. Usually gets used when you use a standard containerised browser testing CI step.

Either way, if someone is still manually testing their website instead of using a standard automated testing system you're probably not really in a league where this matters anyway.. and if they are, you probably have a device farm already.

Not sure where the "my thing is so important, I have to test it on a real device, but I can't pay for it" niche is.