Sorry to hear about this! I have never heard of coccidia being that severe! Did they test him for other stuff too? I would wash everything you had him on and your clothes in bleach just in case before getting another dog.
Read some of the stickies on YT about buying a yorkie and what to look out for- that breeder had a lot of red flags- here's a good one:
http://www.yorkietalk.com/forums/fea...ead-first.html
for future reference a healthy purebred yorkie will probably cost you at least $800, I would be very skeptical of anything listed for less because a true breeder spends much more money on the health of her puppies, parent dogs, testing, and health they don't list them for this much to make money, they are simply recouping costs of care usually