To give a straight dollar figure, a skilled worker doing a trade costs $20-$25 an hour. Covering takes a fair amount of experience to really do well, so that's a good baseline. A simple .40 size sport plane recover will take around 10 hours with someone who doesn't do it alot and allowing for some minor woodwork. I'd estimate a big aerobat with a typical trim scheme at 20-30 hours minimum, more if there are repairs to be done.