Is there a way to evaluate OS X without purchasing Macintosh hardware?
You can't run Mac OS X on non-Apple hardware. It's not allowed by the EULA for OS X and it is technologically enforced by having key parts of the OS in the copyrighted hardware ROM installed in the Apple hardware.  Furthermore, all versions of OS X prior to Leopard and non-server versions of Leopard and Snow Leopard had architectural issues that prevented virtualization even if you wanted to hack something like VirtualBox or VMware to virtualize them in violation of the EULA and copyrights. 

Incidentally, while you can virtualize OS X Leopard and Snow Leopard Server as well as both versions of OS X Lion, the license still limits this to Apple Hardware. 

VirtualBox supports virtualizing OS X Snow Leopard Server. You can find instructions for doing this here.  VMware Fusion supports virtualizing OS X Leopard and Snow Leopard Server as well as OS X Lion client and server versions.