Welcome to the forum.
You could try a Google picture search to try to spot other Bianchis in the same decal style, and you might be able to identify the model. The handlebar stem is recent, the frame might not be. I can't see any tubing (Columbus or Dedacciai) decal on the seat-tube so not sure about that.
Ask the seller if he has any more information. Bianchi have always made a wide range of frames and bikes, of very different quality. A bit like Raleigh in the UK or Gitane in France.
100USD sounds like a lot if it's nothing special, and particularly if you then need to find all the parts to build it up. If you really want a cheap Bianchi try Italian eBay. I recently bought a late 90s Campione d'Italia for 190 Euros here in France, with Dedacciai tubing and Campagnolo Mirage parts, and I've seen them go for even less.
