Meritline offers this Smoke Silicone with Hard Plastic Bumper Case for iPhone 4 2-Pack for $3.79. (It's the second option on the page.) With free shipping, that's $1.90 per case and $4 under the lowest total price we could find for a similar pair of iPhone 4 cases. (However, we saw a single case for $1 less in April.) It's made from a transparent silicon rubber material.

Expect this item to take two to three weeks to arrive.