Need advice about M5
 

To all of you guys on here that own an M5 or are into M5s. I need advice.
I think i am going to keep my M5 and just sell the M3s when i get my new M3. The reason why is because i really love this car and overall i just think its a better everyday sedan than the E60 M5. Plus it is mint condition. Now since im going to keep it its time to start modding it. Its stock now. I already ordered a dinan exhaust and will be getting the new A/A CAI system soon also. But i am also considering A/A's new twin super charger system im just waiting to get a price first to see if its worth it. Dinan SC kit is out of the question at 40k.

But my main question is this. I really want Dinans rear differential with the lower gears. But it i think its over priced. Does anyone know where i can get one cheaper. If i cant get one cheaper somewhere else eventually i will bite the bullet and just get dinans but id rather not. Any help will be appreciated