The $500 Mac mini can handle Xcode just fine, and that is a many year old machine that hasn't been updated. Maybe not if you've been spoiled on better hardware, but it performs adequately.
I used my personal $500 mac mini for full-time desktop and webapp development when employed at Citrix. This excludes the cost of peripherals, of course.
We're talking about a Cordova-wrapped SPA. You can develop those on Raspberry Pis if you had to. A 9 year old $250 MBP off ebay will absolutely suffice.