My family was like yours -- we always adopted dogs for free or a very small fee. When we started looking at buying a puppy from a breeder, we had a hard time thinking about the price tag. We ended up buying 2 Yorkies from the same breeder and the joy they have brought us is priceless.
In addition to purchase price, have you and your wife considered the personality and needs of a Yorkie and whether it is a good fit for your family? Being terriers, they tend to be high energy and need lots of physical exercise and mental stimulation.
While they do not shed like a dog with an undercoat, they do require a fair amount of grooming.
Of all the dogs my family has had, our Yorkies require the most time and energy to take care of. Just something to consider, taking your lifestyle into account.
Best wishes in making your decision!