OK, $200 per season divided by ?? days in the season. Still probably about $2/day or less. It's entirely reasonable if you actually need/use for than 30A (3600 watts). If you don't, stick with a 30A site.
Don't be surprised if the park charges by the site capability rather than your pigtail size. The pigtails have a habit of disappearing after a week or two and the owner probably isn't going to come around for a pigtail inspection every week. If you are on a 50A site and have a 50A power cord, it is often assumed you will use 50A power. Yeah, I know YOU wouldn't do that, but have a calm discussion with the owner/manager. He is the one whose money is at risk if somebody is less than totally ethical.