Check with a local salvage yard and see if they have a used engine that they could install. I would think that they could do this for less than $2000. They should be in a position to determine that the engine they would sell you would be a good one that would last you for many years. They might even offer a warranty. With the problems you described, I am in agreement with everyone else that your existing motor is most likely a goner and not worth spending any time or money trying to fix.