You must not shop for used anything much, because most everybody is "fishing," trying to find that one idiot who will pay their ridiculous price, rather than set a fair price and sell it quickly.
Sometimes these people are realistic, and will accept a reasonable offer. Sometimes they'll run you off their property on the end of a shotgun barrel for daring to offer one red cent less than their asking price.
You don't think that there are any deals, because the deals come and go so quickly that you miss them. The only advice I have is, look more.
Trying to find a specific brand and model of camper, used, in good condition, at a price you can agree to, within the distance you're willing to drive, will be a tall order. You may have to settle for what you can get.
Is being able to stand up in the camper really that important? It's not like you're going to be doing wind sprints in there. You're going to be showering and sleeping, neither of which require standing fully upright. The rest of the time you'll be outside on the trail, or yukking it up with your buddies around the campfire.
All I am saying is maybe take a long hard look at some of your criteria. Maybe you can compromise and find yourself a great deal on a used camper that will ultimately end up being the perfect unit for you.
Putting 10-ply tires on half ton trucks since aught-four.