You can buy mason jar mugs from Pottery Barn.
I'm really not quite sure why anyone would do this. They are $24 for a set of 6, which means $4 per glass, plus tax. Ryan and I buy peanut butter in glass jars for $3.49 from Wegmans. The bonus for the peanut butter jars (besides the peanut butter that comes inside!) is that they work as more than just drinking vessels because they come with lids. I use them to mix salad dressings, store things like beans and spices (I write on them with a dry erase marker) and when they break, it doesn't matter. I have a replacement in the fridge.
The mason jars from pottery barn remind me of a roommate I had for a few months in college. She wanted to purchase breeze blocks (cinder blocks) and planks in order to make herself a bookshelf. I was met with a confused look when I suggested that she purchase a real bookshelf for less money from one of the 50 hundred thrift stores in town instead.