Well if you're buying used there shouldn't be any transportation fees. That's for new units transported from the manufacturing plant to the dealer....
In Michigan there is a $200 one time license plate fee to the State.
There's Michigan Sales Tax.
There shouldn't be any prep fees etc... This used unit should have been reconditioned & checked out before they put it on the lot for sale.
Now if you really want to know what used prices are then go to Yahoo - Google - Bing (etc..) search engines and enter the year and model number of the trailer you're interested in.
Then start your research by checking out all the prices. You also can go to Craigs list and RV Trader to check some prices.
You'll need time to do this.
Happy trails,