Help! How much is the operation to remove a retained testicle on a horse?

Hi I rescued a pony who was pported a gelding, when I turned him out he acted just like a stallion/colt, mounting everything and fighting with my gelding. Ive had a feel and can only feel 1 testicle. I want to try everything to give this pony a permanant home as when not around horses hes a diamond. I cannot afford a ridiculous vet bill for the operation, and havent a clue what to do, PLEASE any suggestions?? P.S no one will take him off me either beacuse of what he needs doing and how he is in the field,Thanks