Not sure what wattage you're looking for but amps under $100...well...you usually get what you pay for.
Maybe this will suit your needs: http://www.amazon.com/Pyramid-PB618-Channel-Bridgeable-Amplifier/dp/B004M9BH3O
Or a little more expensive with the lanzar: http://www.amazon.com/LANZAR-2000-Channel-Mosfet-Amplifier/dp/B005K5KV3Q