Difficult to say. Numbered items are always worth more than their standard counterparts, especially single digits. Lemme do a little spadework and I'll come back.
Okay, I see a lot of single digit hats fetching items like S. Machina which is worth a Bill's Hat. So I would try to get a Bill's for it. The thing being is that these items are expensive, but they seem to move slowly to their cost. So don't be surprised if it takes you a while to find a buyer. The good news is that the item can't be reproduced so it will only appreciate over time, albeit slowly.