Just did my first build, definitely more expensive then planned, but if you have a few basic tools it is totally worthwhile. You will have to but a couple of specific tools, but overall the experience is definitely gratifying. You will gain a good knowledge of the bike, and the build will be as you wish. For 2k or under you can build a great bike. I got everything except the group off ebay. mostly used stuff.

I am also into doing tris, but built a road bike. I purposely chose a more upright road geometry and may eventually throw on clip on aero bars. I thought about a tri bike, but thought that until I really dedicate myself, a road bike makes more sence in the bigger sceme of things.

I am really happy with my build and will build again in the future.