My sister is in the market for a Mac. She's currently using a Dell and is sick and tired of it's unreliability. She wants a Powermac G4, with a CD-RW and about 40GB HD. She says she'd like to pay not much over $500. She'll probably sell her Dell though and just keep the monitor to use on the Mac. Can someone reccomend me some places to buy used/refurb Powermac G4s?