If you want a BSD system, run {Free,Net,Open,Dragonfly}BSD. You can do it on cheaper and better hardware than Apple offers. It just might not look as stylish, but who cares? T-series Thinkpads have better keyboards than Macbooks, and you can still get a used T60 for less than a hundred bucks. (More recent models will cost more, but you'd be shocked at what you can do with a T60 once you get a new battery, max out the RAM, and replace the HDD with a SSD.)
I'd just like to second the used-Thinkpad route. I picked up an X250 (Skylake i5) on eBay last spring for $160, and after maxing out RAM (8GB), a decent SSD and a new battery I'm out ~$350 for something that is both indestructible and quite zippy. Yes, it's not shiny, but IMHO it's a far more practical Unix-y workstation. (I mainly run Linux but I've tested OpenBSD too and everything Just Works.)