Those corner pieces are pricey for sure.
However, I do not think the hardware store sells anything suitable for this application, especially a veneer.
Instead, purchase a piece of PVC board. It is a closed cell foam with a thin layer of pvc material on either side. It is durable and can be painted.
Buy 1/4 " sheet.........comes in 4X8 sheets.
Now when you look at that corner , you may be thinking it is some sort of compound angle, but it is nothing more than a 90 degree bend eith about a 4" radius.
It is "tilted" inward, giving the appearance of something complicated.
This pvc board is lightweight, can be patched and repaired if damaged.
I use starboard, 3/4 , and center cut a dado on either side of a 2" wide strip to accept the 1/4 inch pvc.
This " H " channel is great for joining two sections of PVC or other weather boards.......sometime called dodger boards.
Thru bolt the pvc, or other material when joining with the above mentioned "H" channel.
One other note...........
Bend it with a cheap old wagnor heat gun. ( these are much better than the 80 buck heat guns in tool stores. )
