Sorry, sorry! I have 5 piggies and 50 pounds will last me about 3 months. Sometimes a little less. I have 2 hay racks in each of my cages (I have 3 girls and 2 boys, so I have to have 2 different cages) and I usually put a pile on the floor as well. That way, they have unsoiled hay to get at if they need it and a pile on their floor to play in. I also work all day and by the time I get home, the pile on the floor is gone and they hay racks are about half empty. I refill them when I get home and they're about half gone again before I go to bed. Then they get another pile and refilled again.
There is definitely a difference between 3rd cut Timothy and Bluegrass. They are two different things. But, they will both do the same job. Both are long grain grass hays, which is what piggies need an unlimited supply of. So you can get either one. As far as which one is better, is really a matter of personal and pig preference. Whatever they would rather have, is what you need to buy. Good luck!