Hey, I'm putting together my first system and don't fully understand the amp selection process. what i have is

1. Polk MOMO mm124 12" sub 1000w peak 500w rms
2. 2 Polk MOMO 6x9's mmc690 10-100w recommended rms
3. DEH-P7400MP head unit with 50w x4 continuous output

i'm looking for a good quality amp that i could find used for $150 or less. i know rms should be 500w, but does 2ohm and 4ohm matter? should i amp the 6x9's? how does bridging work and what can i bridge? thanks. suggestions on specific models would be helpful too.