200 watts RMS for 2 channel is way overkill if you're going for a simple cheaper setup. Most aftermarket decks have a 4x20 watt amp internal. I had a 2x60 PPI amp that powered all 6 speakers in my bravada (midrange and treble only), i could turn it up enough to hurt. Plus they were bridged down to like 2ohm which doubles the output.
I'd say 100 RMS will be plenty if you aren't looking for a killer setup. Something like this would work great, and it'll be pretty cheap.
http://cgi.ebay.com/ppi-precision-po...QQcmdZViewItem