There's no way to test on Safari without either buying Apple hardware or subscribing to services like Browserstack.

This is a problem of Apple's own making.

I wish Apple had some sort of "Geforce Now" style setup to run a Mac in a box. I know they'd never go for something like a legit image you could run in a VM, but surely they could come up with something.

My work sent over some old MacBook for when we need to test something unique to Safari, so it's not even the hardware aspect. It's the "I need to find another place to stash a machine, and then wire up KVM switches to use my highly opinionated I/O device choices, on a finite sized desk" factor.