Take a look at these:
Clarion AP-A4204 Profile 440SX Kenwood KAC-748 USAcoustics USX-4065 Just some ideas for you. You should be able to find better prices on these amps if you search around the internet for a while.
You should be able to pick up a decent 50x4 amp for around $150. Getting a more powerful amp for those Pioneer coaxials would just be overkill.
