I found some polypropylene strapping tape at
http://www.uline.com/ProductDetail.asp?model=S-375
and it's about 27 cents per square foot, figuring
both sides, ignoring shipping. I've heard it mentioned
here and people were happy with it.

Long ago on a pond tour I saw someone using polyethylene
sheeting (available in any home store) that they had cut into long strips
(about an inch wide I think). 4 mil PE costs about 1.7 cents
a square foot at http://www.uline.com/ProductDetail.asp?model=S-5130

There is the labor of cutting. Seems like you could cut a bunch at once
with a sharp razor knife. Anyone ever use PE sheeting as filter media?

It's a pretty low investment, I'll probably just try it...