It hasn't been mentioned that you CAN'T get a puppy from a reputable breeder for $500. If they're charging less than that, there's something wrong.
And you can trust me on this: if you get a puppy and leave him alone for 6 hours a day, 5 days a week, you will have a maladjusted monster on your hands in a year. The only people I recommend puppies to are people who are home 20 hours a day, whether they're home in shifts or one is home all the time. I don't want to discourage you from getting a dog. But if you go with your current plan, you will be very unhappy with your dog's behavior and will probably end up giving him away before long. Puppies are very hard work. They're just like babies, if not more difficult! They're cute and sweet, but please remember that when you have a puppy you are responsible for another life; a thinking, feeling, emotional animal. Not a toy that turns on when you want to play with it and off when you're done. And I recently read a national survey of vets about the cost of raising puppies: vet care alone for a puppy in the first year averages $1100!! Adult dogs were at an average of $450. Remember, that doesn't include the costs of training (my basic obedience program is around $300, and I'm pretty inexpensive), food, toys, bedding, grooming, day care ($20-$50 a day), or dog walkers, which would all be essential in your situation.
I hope I didn't offend you, these are just my opinions. But I would not get a puppy if I were you.