take a look at the gun auction sites & see what mossberg 500's are going for, you may be suprised. most 20 gauges i've seen get bid over $200 pretty quick.
i wouldn't pay anyone to clean them up for you, swab the bores & clean the action & call it good. the rough one....i guess it is what it is, polish off the rust as much as you can & price it reasonable. people like me are a sucker for a good fixer upper