Depending on the size of the bottle shape you want.... an extra large rawhide bone for dogs may work, they're pretty cheap, drop it in a bucket of water for a couple 3 days, then peel it apart, take the pieces you want to use and staple them to a board so they dry flat and your off and running, regular 6/8 oz veg tan leather works very well for ball bags, i have made 300+ using veg tan and it holds form very well, can always be jacked to be made harder.