Can't speak for 1/5 as i've never owned or driven one.

$800 for 1/8 is about right with everything minus the radio/rx.

Find out what kind of parts/setup support you can get in your area for 1/8. You don't want to be the only one at your track running that car.

Losi, Hot Bodies, Associated, OFNA, Caster, etc.

they're all great cars that can win, just make sure you can get parts support when things go wrong

Then figure out whether you want to go sensored-Tekin or unsensored-Castle.

Lower kv motor & 5S or 6S seem to be way most people are going these days.

Budget for wheels/tires as well.