> I have had a design that broke only on Safari, and I would be at my wit end on how to fix it if I didn't have a Mac on hand.

I use BrowserStack for it; for just one issue a trail account is enough, if you use it for an open source project you can request free access, and for a business it's relatively cheap.

I've got a pro account for a few of my open source projects; I don't often use it, but have on occasion (for things like you describe, and I don't have a Mac on hand).