If you don't need to increase your braking power any, then the 9" diameter, 5-on-4.5" rotors commonly sold for Street Rods are what you need. They are a straight swap for the factory rotors and use the factory calipers. Cost between $100 and $150 for 2 rotors.
Here is a set on eBay (not mine):
http://cgi.ebay.com/ebaymotors/ws/eB...category=34199
If you need to increase your braking power, the cheapest way is to use early Granada 11" diameter 5-on-4.5" rotors and new calipers and mounts. The calipers are GM-style (Wilwood sells some if you can't stand the GM label) and the caliper mounts are aftermarket. This gets you a moderate increase in braking power (maybe 40%?). Cost is probably $300 if you hunt the parts down yourself.
If you want a major increase in braking power, you have to go to Stainless Steel Brakes (SSB), Baer Racing, or Wilwood. The parts are all aftermarket, and the cost can be pretty steep.