I have about 500 bucks in mine, but I didn't do it all at once. It's a Zebra Tempest, Sparkle Day find. A nice early 80's steel frame with Sugino crank. I rode it quite a while before I decided it would be fun to upgrade. Performance carbon fork, Cane Creek Headset. + stem , $150. Easton carbon seatpost, $40 used, ebay. $200 for a real track wheel set, $15 Textro brake, $20 Felt bargain bin saddle, Dura-Ace cog & IG chain, and a few incidentals. Rides great, less than 19 lb.s. I'd have to spend a lot more to get a better store-bought bike.

My advice would be to start with a good frame that fits you, with standard sizes for BB, seatpost, etc.- stay away from French. Not that they don't ride great- I had a Motobecane- but odd-ball sizes are a nuisance to impossible to upgrade/replace parts. Oh, and for it to really be worth it (and fun) you have to do your own wrenching. I even ghetto-rigged a headset press using a giant C-clamp from work.