A 14' jon boat that has been sitting in the back of a truck is going to be really light. Therefore, the smallest trailer it will fit on will work. Biggest thing to look for is RUST. It is the enemy of all things that roll and go into the water. Lights and bunks can be easily and cheaply replaced. Even springs and axles can be replaced but at higher cost. Personally, I would look for a used PWC trailer. I see them all the time on Facebook marketplace for less than $500 (some as low as about $200) in good shape - some even galvanized.