That won't be easy. But if you make your trip in low season, generally May through August, you'll find the lowest rates. Here's a web site where dozens of camps and safari operators are listed, and you can go to their web sites to see if you can find a good safari place at a price you consider affordable.
http://www.cbel.com/south_africa/ Having said that - good safari experiences will cost $400 a day, when you factor in the costs of getting to and from the camp, tips, some expenses at the camp. Here's a great one, with good May-August rates:
http://www.garonga.com/ Another - April through July:
http://www.honeyguidecamp.com/content_manto.htm
Most don't show their rates on the web, but will immediately respond if you email them dates. Be sure and be specific with your questions about how to reach the camp, and what that costs.