I bought this '04 Trek 4500 last year for $80 on CL and rode it a ton over the Fall and this Spring/Summer. I took everyone's advice here and tried out a bunch of different 29er hardtails but couldn't find anything I liked more than this Trek for less than $2k.
Since I was already so happy (and lucky) with my Trek and how well it fit, I've been upgrading it. Thanks to a lot of patience and serious bargain shopping over the past year I've put a little over $700 into it (including cost of the bike) and it rides like a dream for me now. The only parts that are factory original are the frame, handlebars, stem, and seatpost. Plus, this build made me learn how to install, adjust, and true just about everything with the help of y'all, the YouTubes, and a friend who's a former professional bike mechanic.
Highlights: Fork: Rockshox XC32 TK Solo Air Wheelset: Sunrims Rhyno Lite rims w/ Shimano Deore M525A hubs and DT Swiss 14g stainless spokes Headset: Ritchey Logic Comp Bottom Bracket: Shimano BB-UN55 Crankset: Shimano Alivio FC-M410 42/32/22 Rear Derailleur: Shimano Alivio RD-M410 Chain: SRAM PC-870 Shift Levers: Shimano Acera M360 3x8 Speed Rear Brake: Avid Single Digit 7 Front Brake: Avid BB7 w/ 180mm G2CS Rotor Brake Levers: Avid Speed Dial 7 Saddle: WTB Pure V Race Brake & Shifter Cables/Housing: Jagwire Sport Stainless
Only thing left on my list to replace are the tires, but the ones I have are still good so I'll wait till I wear them out.