Erh... You *know* that "laptop capable of running Mac OS X" means iBook/MacBook/PowerBook/MacBook Pro/MacBook Air, right? Which basically means: 50$ or less is a no-go, unless you're willing to rebuild one from various defective ones (which would probably still cost you more than 50$).
I think it's a ridiculous endeavour. More specifically, though: *ANY* version of OS X? 10.0/10.1 can be run on the oldest of iBooks with enough RAM. Maybe you'll find a working toilet-seat iBook.
Mac user since 1987. Running Mac OS X 10.8 Mountain Lion on a MacBook Air 11" & an iMac 27" and whatever's newest for my iPhone 4s, iPad 3 and AppleTV 2.
Apple Certified System Administrator 10.6, Apple Sales Professional 2008-2011, Apple Certified Mac Technician.