Have seen them in Cheap asChips and other stores alike also some pet shops have them but much dearer although they are stronger .

Petstock always have them in various sizes. Much stronger than the cheapy ones.

I've seen them in large pet stores,but not cheap there. I went to an aluminium sales place and bought a 2.8 x1.2 mtr sheet of security screen mesh. Had it cut in 3 across the width. Gave me 3 pieces 1.2 long by .9 each. Joined them loosely with zip ties. They fold flat and I use a handy wall or fence for a 4th side. Set me back about $70. Very lite & strong.