World of Warcraft Wrath of the Lich King Gamer PC Specs?

[Gamer]

Ok, I'm more a hardcore console gamer, but I've heard great things about the PC game World of Warcraft Wrath of the Lich King so I want to play World of Warcraft cuz im tired of playing Runescape but my computer isnt powerful enough (all my money goes on consoles and console games).

What do hardcore PC gamers such as yourselves buy to speed up your PC games peformance, my budget of items is around $500 dollars.

Please tell me the cheapest but most effective way to boost it just enough to play WoW without any slow down or lag. I plan to join a raiding guild when level 80.

Thanks

Gamer