I am selling TF2 items in exchange for BTC anchored in USD, dictated by the following conversion rates:

• 2.66 refined metal = 1 key
• 1 key = 2 USD
• USD value converted to BTC by current Mt. Gox bid.

This comes down to: 1 ref is $0.75 and 1 scrap metal is $0.0833.  I sell most items as 1 scrap each ("retail" price) but may be willing to do a bulk discount.  If you want, have a look at my inventory.  I don't list keys on that page; right now I have 4.