First of all you REALLY need to find out what your dog has. It sounds like he has giardia (sp?) It is highly contagious. I just went through this with my dog. You also should know what you are giving your dog. I find it strange they didn't do a fecal. Did they check his urine? It is very possible that one of the meds is a wormer, one is an antiboitic, one is for the flora in his intestines and the last one is for his upset tummy.
Diarrhea is not an illness it is the result of something wrong. You need to find out why he has it. If a dog eats something bad then it is a simple cure. If it is something worse you need to fix the problem. Every year I pay $800+ for pet insurance for 2 dogs. Every year it seems like I collect on it. Dogs are expensive. They depend on you to care for them. They can't tell you what is wrong so it is up to you to see they get everything they need.
And no $200 is not an expensive vet visit as far as vet visits go.
Sorry to step up on my soap box but as pet owners you NEED to know what is wrong with your dog and what you are giving him. If the vet didn't explain it to you then you need to ask and take notes if you have to. You wouldn't just take a pill a Dr gave you without knowing what it was for would you
P.s If you just boarded him in a kennel there are a LOT of things he could have picked up.