Hi Chris and welcome,
if you want to buy some upgrades, look at amibay.org first. You can get pretty good deals there + you're mostly buying from people who know how to take care of the HW so it is usually in VGC.
eBay is an option, but the prices there are recently V.E.R.Y. high (PPC card for $1500 WTF?!?) and you're more likely to be cheated by someone.
