I have a transponder that?s not transponding on the selected #'s. no matter what I dial in it sends 1200. They get my alt encoder fine but just 1200. They let me fly in their airspace after I ident, no problem but now just as soon as they give a code and they ask for ident, they jokingly say, "still not fixed huh? Gas must cost too much not leaving any $ for repair. N1200 You are cleared to land runway 28 winds .....................

Embarrassing.
where can I send it for repair or will it be cheaper to replace with a good used unit?
fred