If you are starting from scratch...
1. You could easily spend 300-400 US dollars, or more, on getting a PC that will end up only emulating SOME of the PS2 game library.
2. Or you could spend around ~150 dollars on an actual PS2 system, some peripherals, a PS2 network adapter, an IDE hard-drive, and a FreeMCBoot exploited memory card to load ISOs off the hard-drive.