The reason rescue groups charge for animals is that they have spent $ having them spayed/neutered and UTD on all their shots. I’ve been a volunteer with a hound rescue for 6 years. I can attest that they are not making any money and often times they pay more than they recoup.
The advantages for an adopter is that the dog has been in someone’s home and they can give you information about their temperament, training needs, etc. and they have been checked by a vet. When you walk into a shelter, you don’t have this much information about a potential pet.