Welcome to the group Bryant
Gotta say, unless you are buying a completely restored 1972 Minite FGRV (meaning big $$$) I think that
registration fees may be the least of your investment concerns.
Older, non-restored FGRV's, frequently require at least minimal fixing and, if you can't do it all yourself, it will become a money pit.
Some initial concerns would be:
Tires,($200) any over 6 years old must be replaced immediately, there is a date stamp on each tire. Appliances: Any that you don't see working yourself usually require repairs. If there is a non-op 3-way
refrigerator, and it is original, count on about $600. 3 way refrigerators can't simple be "re-charged" when they don't work. Even a simple thing like a new
battery will set you back $100 and, if there are any
electrical or plumbing issues, you better have an empty credit card to work with.
If the Minit has what's called a "Torsion"
axle, and rides a bit low, that's another big-buck replacement item.
I'd suggest that you find someone that is very familiar with FGRV's to do a total inspection for you and see if you are buying something that is ready-to-go or is potentially a very deep money pit.