LaserJumpStart.com sells stuff that is similar to 1/8 Proofgrade ply–veneer on the outside, MDF on the inside.
Unfortunately you have to buy a lot to get any at all. The smallest order is 24 12"x24" sheets for $144. Shipping to WA is another $30 making the per-sheet cost $7.25. It does not include masking like PG though, and they do not mention a surface finish either… Though they do say you can clean it with a damp cloth, whatever that implies.
Their custom order system will let you order less than 24 sheets but I haven’t looked at the pricing.
The last interesting thing is the stuff can come double-sided, with each side being a different wood and supposedly of high enough quality to be the outside face.
Anyone use this stuff? I am not even sure it’s made with real wood veneer, their site isn’t very detailed.