About two years ago I made one from a sheet of glass.
It worked fine, but I was so scared of breaking the glass I didn't want to use it.
Since then I acquire a Sizzix Bigshot and have found the acryllic plates to work prefectly.
I just got 2 packs or replacement plates and made a new stamppositioner.
Now Sizzix also has cool colors, so you could make a purple, teal, brown or pink positioner if you'd like, I went with clear and am keepin the purple for cutting...bit of a shame though...they're so nice and perfect now....
I have there foam circles from Konad, they're for nail art, but before I just cut up some cleaning sponges and adhered them with souble sided tape to the glass...My cat ate those. ;-)
See video on how easy it is to make, and how perfect it stamps :-D