Your economics teacher will tell you that something is only worth what someone else is willing to pay for it. Having said that, I’ve seen individual maps go for as little as a couple of dollars and as much as $1000 dollars. There are many factors, other than the condition of the item, that can influence a map’s price, particularly on eBay.
This page deals with the large poster-sized maps of Disneyland. There are other types of maps sold or available at the park.
Buying and selling on eBay can be an art. I recommend the following general principles: