400 with TF 240 heads - valley plate options?

The AR Engineering one was what I was referring to in my original post. $175 plus the batwings for $30. Very nice but I was looking for a cheaper option - especially since it doesn't have an access panel. Does it have to be that thick? Would a piece of aluminum sheet with a slightly beveled edges work? Guess when I get the heads, I'll figure something out.