You might look into a Fisher or Western depending on what's being sold in your area. Two stage would be best. Trouble is that usually it's recommended that you put these on a 3/4 or one ton. I have seen them on 1500s around here, tho. Otherwise, you might look into a Buyer's.
Price of salt is going to vary widely. Around here, $50/ton with a three ton min. Best bet would be to find a local distributor and call for quote. Would also depend on how much you buy at a time. 50 tons is less per ton than one or two tons.