1998 Chevy Blazer Vent Valve

Does anyone know where I might be able to pick up a replacement Vent Valve for my 98 Blazer? I checked autozone, they said call a dealer. I called my dealer, they said they couldn't sell it without the fuel tank (~$500), and my local junkyard didn't have any right now. I really don't want to spend $500 to replace a part that can't be worth more than $100 (at the very most). Anyone know a good place to check?

TIA,

Tony

I called another dealership and they sold the part to me for ~$20. Guess I learned to call mulitple dealerships before assuming they are all the same...