Adorbs!
But yes, the younger the dog, the higher the fee, even if there isn't a lot of costs as far as vetting is concerned. Keeps the flood gates from opening. Most people want to "rescue" a female yorkie, under 5 pounds, and less than 3years old, with no medical or emotional issues.
Lily was one of my fosters. She was barely 2 yrs old, almost 4 lbs, cottony teddy bear coat, with the cutest button nose. Her adoption fee was $500, and that was a lot for our rescue. She needed no additional procedures; already spayed, teeth fine, UTD on shots. But she did have emotional stress from young children. Large scar on her back under all that hair.