I just decided to start training for a sprint in june and I'm looking for a new road bike. I have found many with shimano components. I'm on a very tight budget and I don't want to spend too much on my first bike in case I don't like triathlons. I'm looking to spend about $300-$400 (which I know is very low for a road bike). I was wondering how low i should go ranking wise...? I have heard that I shouldn't go lower than 105? Any suggestions?