I made a list in another topic of the things I should have bought when I started, (because alot of the RTR parts failed right away). The list is based off of a hyper buggy. I am not a racer who demands the best parts, but these are items with a good feature/price combination. It is going to be a higher investment up front than what an RTR kit costs, but you won't need to uprade as much later.

http://www.rcuniverse.com/forum/m_3311337/tm.htm