If you have a newer Intel machine, ADGrant's suggestion is a good one (though personally I'd pay the extra money for Parallels; I find it's more user-friendly than VMWare).
But if you don't, I think the cleanest and simplest thing would be to buy the latest and most powerful Mac that can run 10.8
natively, so that you don't need to mess with a VM. The nice thing is they're available on Ebay for $100–$200. [Though you might want to buy in-person, e.g. with Ebay local pickup or Craig's List, so you can run some hardware tests before you buy it.]
Here are your options. These should also all be upgradeable with SATA SSD's (makes a big difference if they're running HDD's) and, if needed, more RAM. If you don't mind a desktop, I'd recommend the Mac Pro as the most robust choice:
Laptop:
Mid 2012–Early 2013 Retina MacBook Pro (13" = MacBookPro10,2; 15" = MacBookPro10,1) (see
https://en.wikipedia.org/wiki/MacBook_Pro_(Intel-based)
Desktops:
Mid 2010–Mid 2012 Mac Pro (MacPro5,1)
Mid 2011 Unibody (7th generation) iMac
You'll just want to practice good hygiene if you're running 10.8, since its last security update was many years ago.