I've been following some guys that post on Beesource for some time that have been building hives, tops and bottom boards from Advantech. Advantech is a engineered sheet lumber that is used for subflooring. Its water proof and doesn't warp. One of those guys on the other forum say they've used it for years and speak highly of it. He has some he's never even painted.
I picked up 3 sheets from Lowe's @$26/sheet. From 3 sheets, I made 15 tops, 15 bottom boards and a 8 frame hive body. That's not bad for $79.
I'm interested to see how they hold up down here. But for the price, it's worth a try. I use MDO plywood quite a bit, but this stuff is half the price.