score:6
I may be off my rocker here but why would you need to buy a car to drive one? There are bus tours of South Dakota:
But I think the simplest option would be to rent a car:
I mean if you have an indefinite amount of time you can certainly walk the Dakotas.
Upvote:5
I meet 3 tourists from Switzerland who where on a 6 months bike tour across the states; if that is your kind of thing and you are up for the challenge. Get a (good) used one and it might even be cheaper than a bus tour.
Or you can catch a lift from Phoenix towards Dakota, meet new people and still get around without your own car. However make sure you don't end you trip in a small village without a bus connection if you hitchhike, otherwise you will have a really hard time getting out of there again :)