Well this is tricky. Inexpensive and strength typically do not go together. Although the Tru Vativ Fire Sl is plenty strong for the price. If you look around enough you can find a good quality Sugino like the 700 or maybe the Mighty for a great price. The bad thing about Sugino is ring life. Great crank for the money just bad rings. I would reccomend Phat Tire. Angelo can hook you up!
http://www.phattire.com/default.htm
Hope this helps.