Question about MAC makeup products?

I use a bunch of random different makeup products....For instance I use eye liner from Mary Kay and the unstoppable brand. I also use several different brands of eye shadows, blushes, and foundations. Mostly I just like to experiment. I have heard about a lot of people using MAC makeup products and I was wondering how good they are. Also, are they super expensive? Where can I buy them? Also, can you sign up to sell them like you would with Mary Kay or Avon?