Agreed with nickrac, prices can vary quite a bit depending both on the number and also the extension. In general though, as there are only 300 of them they are quite valuable.
I saw 31.net got to over $700 the other day in namewinner. I do not know if they got the drop. Buydomains end up with the name so they probably grabbed it using there resources. It is for sale now at "request a price". Yawn. Moving right a long.
Someone offered a two character (letter and number) in the for sale section at the buy now price of $1750.
A nice two number or 2 character can be a gold mine if you find the right buyer (read deep pockets). I'd be surprised if an ordinary 2 character/number went for below $500.