What website would have the cheapest prices and good quality parts?
Probably Chain Reaction Cycles and JensonUSA. There are plenty of others on eBay, or ones that come up if you Google search a part (sometimes even Amazon.com).
But, you can also have your local bike shop order from a distributor like BTI. Some local bike shops are worth supporting. It might be a little more expensive, but sometimes you get benefits back in other ways--like the shop helping you ship a bike, etc. etc.
Our LBS owner will do IOU's and discounts as my friends and I are loyal customers.. Definitely worth making a friend at your LBS! But as cmc4130 said Chainreaction has prettymuch any part you could need for a pretty decent price most of the time