If I plan on keeping my boat in the water(on the intercoastal), should I put bottom paint on it? How much would something like this run for a 20 foot outlaw? Will it slow down the boat as well? Thanks!

Just painting it isn't the solution....you have to prep the bottom properly first. It will also slow you down 3-4 mph. I have done this on cruisers several times, and would recommend a lift of any type for a perfornace boat.

Keeping a performance boat in the salt water is the kiss of death.

Dude, don't do it! Buy a trailer even if you have to pay for storage. You'll never be able to sell that boat once bottom paint goes on.