For the meds that a vet will write a script for, I use Dr Foster and Smith, online. Basenjis are known for thyroid problems among breeders, and many vets will not acknowledge this. So, I take my dog down to the vet I originally got my dogs from, she examines the dog, and writes a script for the thyroid pills.
One of my dogs recently went on seizure med, a human drug will do the best. The vet wrote me a script and said people seem to find Costco the cheapest. I found out you do not have to be a member to use the pharmacy. I noticed, back in the pharmacy, they have a big sign about having meds for pets.
For heartworm preventive for the dogs, I buy from Dr Foster and Smith and buy the swine ivermectin. My vet knows I do this, is obligated to tell me he can't advise it, I tell him I understand and thank you for the info, and the subject is dropped.
I do not give them low quality food, found something that worked, and have been using it since. Cheap food, in this breed, causes many other medical problems.
I buy Nutro Ultra, 30# for about $40. I think it's from the same company that makes Iams. I buy it at a locally owned hardware shop, I don't think grocery stores sell it.