Depends on how rusty, condition of the tranny, etc.
For the picture I formed in my mind, $500 tops.
Depending on how bad the engine is stuck, you might be able to free it by pulling plugs and putting some good penetrating oil down onto the cans, it may soften the rust enough you can break the pistons loose by hand cranking the engine... I know many who have done this successfully.
Good luck, keep us posted...