Struggling from the pics. It looks to me as though the tubing is round, not the classic Master 'Gilco' quatro-foil shape.
The paint scheme I think is AD11, with the little racer on the top tube.
I had a C40 in AD12 (Blue). The AD colours weren't illustrated in the 2004 catalogue (may have still been available, particularly through Maestro).
I would suggest the colour scheme is a late 1990's / early 2000's. The two steel models I recall from that era (other than Master derivations) were the 'Classic', which was offered until mod 2000's, a basic (can any Colnago be called basic?) steel model, with chrome lugs at the head tube, round tubes and similar seat tube/ seat stay lug.
The other, better quality, lighter weight (I think there was rider weight limit of around 180lbs, from memory), steel frame from the era was the Tecnos, made I think from 1996 to 2000.
Colnago colour schemes were supposedly hand painted and varied one from another. The Tecnos frames I've seen had 'Tecnos' on them. Given the variation, this is probably not a definitive way of determining if yours is or isn't a Tecnos.
On the balance of probability I would be inclined to think a Classic is the most likely model.
Value - what is the condition? Are you looking to sell the whole bike,or just the frame?
About four years ago I sold a nice steel Colnago and forks (early '90's) for just under £200. It was a 62cm, which may have limited the market, but still - depends whaich buyers are in the market, eager for some Italian exotica when you come to sell. And Colnago fits the Italian exotica in most peoples books!
How long have you had it, what condition is it in, do you know any more of its history?