Saw an 1835 VW engine for sale locally for $1200, no fan or shroud or generator. It's not converted for aircraft use, but was wondering if that's a fair price. It's on an engine stand so it can be demonstrated that it runs.
There are just so many variables it is nearly impossible to say if it is a good deal. In the final analysis the definition of a good deal is up to the individuals involved.
You need to know specifics about the engine like:
Is it bored for oversize bearings. If so what size? Was the thrust surface cut as well?
Was the case checked for spread center main before it was bored?
What size head studs are used? 10mm? Pass
Crank: Turned undersized - if so how much?
Valve train: All new? What cam grind?
Heads: Rebuilt? If so what size valve guides were used and how deep are the valve seats compared to new? Did the person doing the work do a proper job?
If you have the answers to these, and other questions, do you trust the person telling the story?
If it has been run on a stand with no fan shroud, or other cooling fans - keep looking.
A Great Plains 1835 kit is about 3 times that price - but you have a pretty good chance you are getting quality/new parts.