It can get very expensive. I wrote a Creative Labs Speaker hack if you want to go the cheaper way...sounds very good
No, no, no. I have abandoned the idea of budget speakers now. Everything else on my cab will be translucent, so now that I know they can, speakers must be too.
I chose to run them though my receiver putting 120 watts per channel at 4ohm with a 300 watt BASH amp (4 ohm) for my subwoofer. Built in a 4.0 ^ 3 box tuned to 25hz. Sounds fantastic when playing the jukebox section of the cabinet...oh man you should see my home theater. 
The home theater is a whole different project. I may hook up the cab to the home theater and use it as a jukebox, but I wouldn't be running the cab speakers then.
I found the 5's for $79.95 and the 4's for $69.95 each in a local dealer's shop. I don't know which size I'm going to do with yet, but do those numbers sound right to you?
Update: Never mind, Crutchfield and Sound Domain have them for $55 a pair with shipping.