Festivus
First Post
For squares, I think a cheap metal rod (coat hanger) and a pair of pliers would be easy enough to do. Most hardware stores would carry such things. Although, those prices for the plastic ones seem reasonable enough to me.
Bending coat hangers so they are square and flat is not as easy as one might think (speaking from experience). I will say that the 3.5 ones are life savers... for 4E I am still not sure. We have found that a simple Post-It stick up happens to be 3 inches square and holds it's position nicely on the battlemat.