It is impossible to answer your question properly unless you provide more information. What is the year, model, mileage of your car ? Is it in or out of warranty ? Where do you live ?
Car repairs are not priced by the type of car you drive, but the labor rates are charged per hour based on the type of repair shop that does your work. A dealership has the highest hourly charge, and a corner ASE mechanic has the lowest. Shop rates vary from city to city, state to state etc.
As for parts, you can put any kind of tires you want on your car. As long as the size is correct, you can go to Walmart and put a no name tire on it, or you can go to a performance tire shop and put a Pirelli tire on it.
Here is a link to one tire retailer, where you can shop by size or type of car.
If you want more information, please answer my questions.
If you have an all wheel drive, even if one tire is flat you will end up changing all the four tires to maintain thread life/alignment. To change all 4, it may cost you close to 800$. It always helps to get the tire warranty on BMW's if you can.