Not sure how much is it gonna cost to repair the USM, but standard base price for lens repair is $269. Additional parts will be more, for sure.
I just had my 35L fixed a week ago. They opened up the lens, recalibrate and cleaned. All done for $269 and it took 2 days.
I also had my 40D fixed. They replaced the shutter assembly, the AF module, and the shutter button all for $209 (standard price to fix body, I think) and took 2 days as well. You might get lucky and get the USM replaced for $269. Good luck.
So you get the idea.