A non-running van might be worth $1800, IF the rest of the van is very nice and in good condition. The problem is that any vehicle that sits for a long period of time will have problems with ruber seals drying out, belts and tires rotting, gas evaporating and sludge clogging the fuel system, brakes rusting up, etc...
Additionally, a 1986 Dodge van will have a slant six motor with some form of Chrysler's notorious "lean burn" computer controlling the carb and/or ignition. The slant six motor is a great engine, but the lean burn computer was a por design and was often faulty when new. parts for the lean burn system are getting expensive and hard to find. It is entirely possible to convert the engine to an older electronic ignition and non computer controlled carb, but you will have to do that stealthily to still pass CA smog checks. It can be done, but you will have to be careful about it.
I would want to know why the seller thinks the engine needs a rebuild. Many times the lean burn computer will make the engine run very poorly. The slant six is a very robust engine and very often people think it needs a rebuild when reall it just needs a good tune-up. It might be that converting to non-lean-burn ignition and carburetion solves the problems with the engine and the van will be good to go.
If you are really interested in the van, hea over to www.slantsix.org
and see if one of the California members would be willing to look at the van with you. There are some very friendly and knowledgeable slant six owners on the site who would probably be happy to give you an honest opinion.
$800 back fees on top of the other potential costs is a pretty big cost. I would find out as much information as possible before eciding to buy this van.
As has been said, there are many other vans out there. This might be a big can of worms and not worth it unless you really like the van and it is cosmetically in great shape.