normally beginners rackets are light and large. but if you're playing competitively then i guess you'll be looking to improve and seeing as you're young, then a true beginner racket will do you no favours. you'd probably be better off with a tweener racket, which may be a little harder to use at first, but will help you develop your strokes and technique better.
if you're looking to spend around 100 bucks then it you'll be looking at slightly older models and the best place to get it would probably be http://www.tennis-warehouse.com/catpage-liqracs.html
. some good ones to look at would be head liquidmetal 4, wilson ksting 105, wilson kzen team. personally, i would recommend the kzen team; its still in wilson's current line and is a rather underrated racket