just add. Of course, yorkie mixes are popular, but still many of them in shelters. I know one rescue in our state who REGULARLY bring SMALL designer breeds from hi-kill shelters in California, because just too many of them. You can easily find them on petfinder.com
And on top of that, you will get already fixed/microchipped/UTD all shots for price less than from a breeder. Breeders sell mix pups only. All vet expenses (spay/neuter. etc.) will be on you.