mono 2 channel or 4 channel

[Blazer Eagle]

hey i know this is discussed alot, but i really am not an audio guy and it really confuses the piss out of me, i plan on putting two 12" subs i nthe back of my blazer, 500 watt rms 1000 peak and 4 ohms (http://www.millionbuy.com/bosd12f.html i know they're cheap and crappy but i like the price and the depth) i also have two 4x6's and two 5ish inch speakers

ive been thinking about either running just the two subs of a mono amp and the others off the head unit, and of putting them all on one amp, whish is better?

and what amp should i get, besides channels what wattage should i get?

im going kinda cheap, so im looking mainly for under $150 for the amp, any advice?