I think the best reason to not get the pet store puppy is to remember where it's parents are right now. This little puppy at the petstore will find a home, but it's parents will never get that luxury.
This is what I remind myself each time I go into a pet store. I know we want to rescue every pet store puppy, but by rescuing them we only add to the supply and demand of the industry.
Have you ever seen the website
www.prisonersofgreed.org ? That might reinforce your decision to pass on this pet store puppy.
You can definitely find a quality yorkie in your price range with some patience and determination. Or, could you possibly wait until you have more saved?
I have 2 puppy mill puppies and it weighs heavy on my heart daily knowing I supported that industry. But, what comforts me is knowing that I will never do it again. I will never shop in a store that sells puppies for any products and will not give them a cent of my money.
Some rescues will work with you if you have children, it all depends. Even though I know it is hard at times to get approved by them. I don't even have children and it was hard for me to become a foster parent, even.
As far as your question goes, I had a horrible time housebreaking my two puppy mill puppies. They think their crate is the correct place to go, so crate training is super difficult. My lhasa would go to her crate to pee, and it is still taking us work, after 7 months to break her of those habits.