While it's true that ALL chins are deserving of a loving home, it is also true that a fat, healthy chinchilla from a breeder is going to cost a lot less than one from a petstore.
When I fell in love with Mr. Whiskers in July, 2004, I paid $139.99 for him in a small petstore in Evanston, WY. He was smaller than I now know most chins are. I believe he may have been the runt of his litter. Two years later, I paid only $75 for The Snuggler, a fat, healthy baby who came with a pedigree from a breeder (Riven) in Nebraska.
I love both of my boys, so I would never discourage you from wanting a chinchilla. God knows, they quickly endear themselves to you and become a large part of your life. If you are in love with the petstore chinnie, then by all means take her home, but definitely have a vet look her over. If you are able to, go visit some breeders in your area, or attend some shows. Once you see the difference in size and quality, you may change your mind.
Good luck to you!!!