On my high school tennis team, we have a lot of heavy hitters which is why as soon as the coach is done stringing one racket, another three is thrown at him. One of the more economic strings that lasts relatively long and plays decently is the Prince Lightning XX. I've strung with both the 17 gauge and the 16 gauge, and I can't say that I can notice a huge difference, in fact, any difference at all is probably coming from what I hear from other plays on the board, rather than what I experience myself.
It's not a very expensive string, it's a synthetic gut I believe. The Prince Lightning XX is a decent string if you're breaking strings too often.