This is one of my favorite AG costumes, ever. The material is so soft, and all Bitty dolls look uniformly adorable in it. I especially love the twee paws and perky tail! However, I am mystified by the choice to use a zipper instead of Velcro closure. The zipper never quite stays up under the chin, even with the collar to hide and reinforce it. The zipper is an odd choice for a company known for its Velcro closings, and is annoying enough that I think it brings the grade for the outfit down to a B++. I bought this outfit when it was on sale through AG, so I can't speak to its availability on eBay because I've never bothered to look, but it originally retailed for $24 and was marked down for a while IIRC.
Photos below are on Bitty Baby but it was originally marketed for Bitty Twin. The outfit works fine for both lines.