I think I paid about $500 to have the rough resealed on my Bigfoot, I suspect most jobs will be between the $500 and $1000 range. I once had to repair my fridge vent cap and manually scraped off all of the old caulk myself. I had no idea how difficult and time consuming that task would be. I spent hours on my hands and knees trying to scrape it clean before applying new sealant. That experience led me to pay someone to reseal the rest of the camper.
I suppose there are a few tricks to help get rid of the old sealant but for me the cost of paying someone $500 to do the whole job was worth it. I'm not one to shy away from projects either unless they are tedious and back breaking...