Recommend that you read 2 very valuable Sticky's located at the top of this forum (it will help to explain some of the cost differences):
1. Wheel Manufacturing Methods: http://www.m3post.com/forums/showthread.php?t=357430
2. Wheel Standards: http://www.m3post.com/forums/showthread.php?t=353224
You will have to spend a lot of money to beat the overall quality and value of the BMW OEM wheels that are available for the M3. The Morr VS8.2 appears to be a good value as do Advan and Volk wheels. If you want to spend real money, you can't go wrong with any wheel manufactured by Taneisya (Dinan, Neez, RAC). All of the wheels I've listed are certified to meet either the JWL/VIA or TUV standards. There are other good brands. JWL/VIA or TUV certifications, or extensive track use with lots of user feedback are important indicators of a quality product.