Since it is very very common for Yorkshire Terriers to have retained puppy teeth, it is recommended that they have their first dental done at about 8 months when all the teeth are in, but before crowding, bite issues and tartar build up can really start. I have all mine done at that time, and all but one of mine has had deciduous teeth (extras).
The cost on this routine, usually runs about $90 for the anesthesia, cleaning and $10-$20 a tooth pulled plus $15 for pain meds and another $10 if they need an antibiotic
Hope this helps. Other areas are much more expensive I understand but Central Florida is a bit cheaper.