what kind of bike for sprint triathlon?

[Brady C]

I'm training for my first sprint triathlon in a couple months, and I'm trying to find a bike that will at least get me through the first one. If I continue to do it I can look at more expensive ones, but my budget for this first one is pretty limited, under $200. One question I have is, do you have to use specifically a road bike? I've never used one and I'll probably want to take it on some trails too, not hardcore but rougher than I would imagine a road bike would be used on. What kind of brands should I be looking for? What should I do to a mountain bike to make it triathlon ready? thanks