Well you will get some good info from one of the real Pit people here, I know.
First - your friends' dogs did not "mate unintentionally." It was quite intentional on the part of the dogs, and quite silly of these people to allow it. I don't think they deserve any money for making a silly mistake and pumping yet more pitbulls into an already overburdened population. If I somehow wound up with a litter of "unintentional" puppies I would not seek to make one dime off them. I think I'd require a hefty little donation to a rescue group or something instead, just to keep an ethical balanced karma thing going.
(There. Got that off my chest!)
Anyhow, you will often find pitbulls, including puppies, through rescue. I'm pretty sure LuckyRescue will be able to fill you in there. Rescue dogs are usually UTD on vacs, and always spay/neutered.
The total cost of s/n, shots & vet care shouldn't be terribly high in any case - a few hundred $$ depending on your vet, over the first year. 8 week ob classes typically run $80-$100US; again it depends on your location.
There's quite a difference between a Golden and a Pit!
Some downsides to Pitbulls:
They are often dog/animal aggressive, though typically sweet with humans. Many municipalities have breed bans or restrictions. Many (if not most) homeowners insurance companies will not insure certain breeds - Pitbulls, Rotties, Chows, Mastiffs, etc. This will make it *extremely* difficult to find rental housing, trust me on this one! I've had Rottweilers for...almost as long as you've been alive, yikes. Back when I was renting, I figured that I was restricted to less than 1% of the rental market. This may account for ads for throw-away dogs that say "moving must sell."
Plus the public perception of the breed is such that you will be critisized often for having a "killer" breed. Plus they are pretty high energy dogs, I think.
Not trying to put you off, just trying to provide a reality check! I adore Pitbulls; I've had a few fosters. Great dogs, extremely smart and I really like their appearance.
Also - puppies are an enormous amount of work to do right. And some breeds are going to be a bit more challenging - I'm guessing a terrier-type dog will be among the "more challenging" category.
Anyhow - I think your thought processes are leading you down the correct path! If you don't go through rescue (best option) then someone who has put some care into breeding healthy, stable dogs would be the next best thing. Same goes for Goldens, too, BTW. Goldens can have quite a few health issues - epilepsy is one I know for sure - that can be very expensive and difficult to deal with in the long run. I have neighbors with two poorly bred Goldens, 3 yo littermates. One has epliepsy and both are in generally poor health - allergies, frequent infections, like that. I've been trying to persuade my neighbors to change diets, but they're not going for it!
