It's Starbucks. There are 3 located in the MGM Grand, 1 location being 24 hours (which is pretty amazing, IMO). I don't think the prices are any more outrageous than any other Starbucks I've ever been in.
If there is a large convention in the hotel, the line can be VERY long (especially in the morning). So be prepared to wait.
The service isn't exactly extraordinary, but it isn't horrible either.