DJ, here is a chart from Lake Country. I have used their pads since I've started. I have the 6.5 with the velcro backing. If you want the plain flat pads, Auto geek has a great close out price, $39.99 for a six pack of orange(light cutting) or white(polishing).
You can re-use them. You will want to get some cleaner and a tool. I tried to soak and wash them out the first time without those and you just can't get all the produtc out.
http://www.lakecountrymfg.com/2006ApplicationGuide.jpg
http://www.autogeek.net/vcpad.html