I like arnswine's suggestion. Trade for Chores is a good idea.
$100-200 bucks for an engine that turns freely is about right. If it runs, then it will be worth more (probably $300-400), but it sounds like this is not the case.
I really won't comment about the body. a fair price will depend on the amount of rust and what kind of shape it's in. Maybe if we saw some pictures...
