How much would a used engine for a 1988 ford Step van Cost?

I am interested in buying a 1988 step van that they sell to me for $350 dollars. It needs some work paint job and stuff like that but the thing that i am most concerned about is that the carburetor is missing or its to big and it "backfires"? Is the engine bad? Would this be a good deal in the end if i decide to purchase it? (F.Y.I -i would like to use the van in transporting my dj equipment from events)