A new crank is about 4k or so.. If you're not planning on overhauling the engine or splitting up the engine before flying.. it would make no sense to buy it.. If you're gonna pay someone to swap cranks for you, you're looking into 5-7k in labor alone.. So, total -- 10-12k to just swap cranks.. assuming everything else is in great shape.
Doesn't sound very economical to me...