Triathelon or not - What kind of bike do you suggest?

JuberP

Hi Ladies-

I would really like to get a bicycle for exercise.  A few summers ago, I would get on and go - 15 miles or so - and loved it.  I had a Gary Fischer, with thick nubby tires, but (I don't think) had much suspension for mountain trails or anything.  For the most part, I really liked it. 

I'm toying with the idea of training for a sprint triathlon, but in case that idea goes the way of the dodo bird, I don't want to buy and overly race-specific bike.

My question:

1. Do you have to have a road/racer bike for a casual sprint triathelon? 

2. I don't want to spend a whole lot of money ($3 - 400 as the absolute highest), is there a bike you'd recommend?  Until now, I have been thinking of just heading to Target and picking up something.

TIA!