Newbie ISO bike

I'm new to tri's but regularly compete in open water and running races. Just got suckered into signing up for my first two tris! One sprint and one Olympic. I am looking for a very low cost alternative to riding my Huffy Mt. bike from 2002(not even joking). Im located in CT - any recommendations on where to even start looking? The local bike shops couldn't get me on anything for less than $450. I'm 5'5'' and I think I am looking for a 52 or 53cm. Any thoughts recommendations and advice on a used bike would be most appreciated!!!!