I am running 50 amp service to the end of a 900 ft' dock. I am told that I need two hots, a neutral, and a ground. What is the cheepset size wire to run, and where can I get it. Thanks Rodney

What size wire are you planning on?

Will probably be a large size, so aluminum wire would be the cheapest.

Will this be in conduit?

Large size wire would need to be purchased at an electrical distributor.