Welcome to the world of Tris and endurance sports.
I have a slightly cheap (comparitively to a $3k-$5K tri bike) Trek 1000 road bike with aerobar setup. It has gotten me where I want to go so far in the Tri world. My baby (that I won't get rid of) is a very older model MTB hard tail that I love to death. It is the billy goat of bikes.
My MTB is the bike I used for my 1st Tri (a sprint). Don't soak too much money into this sport until you know for sure that you love it too death, and even then you must be careful. It is truly a gadget, hi-end kinda sport. Stay low-end and have fun in it for a bit.