Some people around here thing 20ft jumps makes you a "Pro FMX rider"... Just ask them. I'm sure there's 1400 threads that they've started around here proving how badass they are.
Anyways, as far as going back to stock, that is all personal preference. If you were happy with the way the bike was performing before, than I say just keep it stock. Are you replacing the crank because it NEEDS to be replaced? or just because that's what the shop told you?
Prices for repairs are going to vary by region, but I would strongly suggest sending your motor to one of our site sponsors. They all specialize in Banshee motors, and I can almost guarantee they will be cheaper than a dealership. You will get a proven product, and the best customer service anywhere.
I see you are in San Diego.
Call Kevin Herr from Herr Juggs racing. He is in Encinitas, I believe, and has an extremely fast turn around time, and does incredible work.
Website: http://www.herrjugsracing.com
Contact: 760-815-1316