Rosa, this place has good prices on puppy pads. I don't think you would need the premium ones - you just need a pad so it doesn't get on anything, right? With urine, the heavier pads are better, but since it's for poo, you could get away with the cheaper ones.

If you have Costco or Sam's Club, they have really good prices on pads too.
Samson, GSD, 10/13/07
Annabel, Keeshond, 4/21/11
Petie, Toy Poodle, 5/5/07
Kitties: Meezer, Bob, Mia and Dewey