Are you sure it's your crank? Sounds a lot like a problem I had. The grease on the threads between the pedal and crank arm breaks down eventually and leaves the tinyest bit of play between the threads on the pedal and crank arm, which causes a creaking sound. In my case anyway. The 2 suggestions I got were 1. Teflon tape around the threads. 2. Anti Sieze on the threads. I opted for the anti sieze and it worked great, I've used it ever since without a repeat of the noise. Might want to try that before you replace anything, anti sieze is only like 4 bucks. Good luck.