Generally it will be $400 to find the leak, install Schrader valves and recharge the unit when done properly and at the most yo might get a 30 warranty on the work done.
Personally i would replace i, but I;d do it my self. Shop on line fro new units to get a feeling fro the price. It is a 1 to 1.5 hour job by decent techs.
Amateur Radio Operator (KE5DFR)|Full-Time! - 2012 6.7L Ford Crew Cab Dually -2013 HitchHiker Champagne 38RLRSB - Travel with one Standard Schnauzer and one small Timneh African Gray Parrot