How much would it cost to swap my engine?

How much would it cost to swap my engine?
Added (1). I have a 84 honda nighthawk 650cc. It had an oil leak and the engine blew. I have found used motors for the bike at 500 bucks, I was curious as to how much money (roughly) would it cost to get a mechanic to replace it for me. Also if it would be easier to replace it myself. I am not mechanically inclined but I can learn. I live in new york city if that makes any difference.

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