Depending on exact make, model and condition, anywhere from a fiver upwards... Cinelli in good condition I would say 20 or 25 quid each? Need photos though as model and condition can vary the price a lot
I'd suggest value depends on market. I tried to sell a number of 42cm Asian manufactured vintage drops locally and had 0 interest. My feeling is that where a 26.0 clamp bar is wanted people are typically interested in maes style profiles in wider widths as per current trends.
As above; it depends on what you have. Width, shape, model and diameter at the stem(25.4mm, 25.8mm, or 26mm) all *cough* steer the pricing. Scoring to any part of the bar massively reduces prices as such bars are destined to be placeholders/pub bike bars/test a width and shape bars.
A good while ago I had trouble shifting three pairs of Cinelli. No interest even with very low prices.
As a last attempt to get rid of them I advertised them as a job lot (where postage costs makes much more sense) and they sold immediately to a small specialist bike shop.