Expensive plywood

So, I just got prices for the Baltic birch marine grade plywood
!!!
At $170 per sheet, I am looking for alternatives. I am planning to insulate my walls. Fiberglass will finish the outside, so neither side will be exposed.
Can anyone suggest something less expensive that will hold up?
Ted

At $170 per sheet, I am looking for alternatives. I am planning to insulate my walls. Fiberglass will finish the outside, so neither side will be exposed.
Can anyone suggest something less expensive that will hold up?
Ted