Go to http://ytca.org/mainview.htm and check out their breeder referal program. Breed club are a great way to learn about different breeds and find breeders. Every AKC recognized breed and most "real" breeds have their own parent club.
Please keep in mind that "reasonably priced" Yorkies may be cheaper for a reason. MOST of the time the reason the price is lower on a dog is because their breeder is cutting corners so therefore needs less money coming in to cover their costs. No breeder WANTS to lose money. Reputable breeders rarely do more than break even - but we don't usually go into things planning on taking a big hit on the litter.
Lower priced dogs are usually possible because the breeder is breeding dogs they bought from a Puppymill or BYB who didn't charge THEM very much. And it's usually less than they are asking YOU BTW... If they are breeding low quality dogs, don't test, don't feed a good food, and don't provide good vet care they can shave a couple hundred dollars off the price.
Your best bet is to find out what most reputable breeders in your area are asking for a Yorkie. Then budget it in. Don't settle. You'll make up the price difference on the cheaper dog later by paying it in vet bills...
And honestly, I worked as a groomer for a short while... badly bred Yorkies are a NIGHTMARE. They are usually snippy, yappy, unpleasant dogs... well bred Yorkie's are sweet, really pleasant dogs... good breeding makes a big difference!
I missed the part about reasonably priced. Abby is right, bargain yorkies should be avoided. A $500 dollar yorkie could end up costing you another $3000 for knee surgery. It varies by area and gender, but a good yorkie is probably going to start around $1000. Of course just b/c a pup has a high price tag, doesn't mean it comes from a reputable breeder. A lot of the puppymill and broker websites sell puppies for 2 or 3 times what a reputable breeder would charge.
Oh, please, if you need a 'reasonably priced' dog - adopt one from a shelter! They're great dogs and many will not survive unless they get adopted! NO breeder who's worth his/her salt will sell dogs for a bargain - there's a LOT of work that goes into breeding - they check their family trees, they make sure that the mother and father dogs conform to the breed standard (so you don't have $$$ medical problems down the road), they have them vet checked for their breed's particular health issues - they all have them!
Oh, and DO NOT fall for the TEACUP yorkie bull. An extremely small yorkie is not worth more, or a bargain. There are NO teacup dogs-that's a designer name. The extremely smal ones are in fact the underdeveloped pups in a litter. They tend to be the ones who were conceived after the others since dogs breed several times. Ahd they can conceive new pups over the receptive period,so you have puppies at different developmental stages when they are born. Also don't pay more for an unrecognized color. A yorkie should be Steel blue and tan. They can be varying shades of it but should not be obviously not blue/tan.