http://ekizo.mandarake.co.jp/auc_e/item ... 7720100002
But ... the auction description isn't accurate:
Kero's Corner production cels have gone for very high prices: two of the top ten prices paid for CCS cels on auction were for pan cels of Sakura in battle costumes used in this episode-ending feature (the Ep. 24 "Alice" costume and the Ep. 8 "Pink Kitty" costume, both for over 300,000 yen).with a certificate /TS/with doga /total collectin of "kero corner"
The problem is that the "Kero's Corner" (Kero-chan no Omakase) was discontinued at Episode 34, so there was no such feature for the episode where she wore this costume. I'm up at my campus, with my Sakura Cards TV Animation Art Book 240 miles away, but I feel pretty confident that the pose is the same as in the color settei section of this volume. I'd guess that it was originally a color test, like many that have popped up for sale.
Perhaps it was used as a sort of hanken in the Art Book and so it deserves a bonus price. But, despite the certificate and the sequence number in the upper right corner, it's not a production cel. Bid accordingly.