i'll save you the trouble of using the search feature for a race upgradable chassis for a decent price and komes with decent stock stuff you will find three answers (with will find more but duratrax and traxxas don't count when it komes to race upgradability)

RS4 3 RTR is great very proven car engine is lacking

RS4 3SS a little more expensive than the RTR needs radio equipment but the engine is a nice powerhouse

TC3 RTR great car cant go wrong with associated and the engine is somewhere between the .12SS and .15FE that come in the RS4 kits

if you want to wait HPI should be putting out the RS4 4 sometime by the end of the year but other than that without getting into exoctic brands like yokomo and the kyosho v-one series these are some of the best setups for the price and have a slew of upgrade and replacement parts usually found at your LHS. I know i am gonna get flames for the duratrax and traxxas comment along with brands like tamiya ofna and the gp kyosho series but lets face it if you started a poll the top two cars would undoubtly be the HPI rs4 and AE TC3