I've chosen a head unit and 6x8's - now what sub/amp combo??

I am pretty much set on the Pioneer/Premiere DEH-7700MP/770MP head unit and I will be getting 4 pioneer 6x8 3-way speakers. Now I need something for the low end rumble. I want something in the $100 range for the sub and maybe $150 for the amp. I am looking at JL and Alpine subs and Alpine and MTX amps. Each one of these are about $100 each at my local stereo shop.

Any advice and insight would be appreciated. Thanks.