Well, you would too!
I’ve just looked at the tutorial for making HDPE clamps and thought “I can do that, and they would be useful”, so trotted off to Amazon to look for a board - then almost fell off my chair!
The smallest sheet nearest to 1/2" thick is 1m x 1m x 12mm and costs £140 (about $180!).
I think I’ll use 18mm ply - as I’ve got shed loads of it!