A local guy has a Diamondback Ascent EX Adventure Series for sale for $40. Im just getting into mountain biking and it looks pretty decent. 18 speed, No suspension, 24" steel frame, 26" tires. Is it a good bike? Reasonable price? and will it fit a 6'4" guy? lol Also, how "upgradable" is it? Like if I wanted to put on a new fork with suspension, disc brakes, new derailleur, rims, hubs, etc, how would this factor in? Are the upgrades somewhat limited or is it really not upgradable at all? Sorry for the n00b questions.