Nobody said that your BP needs to go to the vet once a month. I am rather disturbed by your statement, though.You would rather have fun, than prevent the suffering and possible death of your BP? Please correct me if I read this wrong or interpreted it wrong.
If you really feel this way, that riding horses is far more important than caring for your BP, then I would recommend finding your BP a new home. I'm not trying to attack you, and I do understand how fun horses are and the limits of teenage allowances but if your priority is showing horses and not the well being of your BP, it will be in the BPs best interest to go to a home where the owner is not so 'strapped for cash' and has the time and willingness to care for the animal.