Do you know a doctor or nurse?  I'm not sure the legalities here or if the medicine you are using is a prescription med (for people or pets).  However you may be able to get a human product cheaper...believe it or not.  

Is your dog a purebred?  If so, check if the national breed club has some sort of health program that can offer assistance. 

Also talk to your vet about the amounts currently needed and if there is anyway to cut down on it without affecting the dogs health.  I assume the special food is one sold by the vet.  Many times there are homecooked options that are cheaper.  And the amount of added enzymes may be able to decrease over time as well. 

Best of luck to you!