Hey.
I'll second the Woodwind Exchange in Bradford call, although I went there today for my monthly visit, and was deep in conversation with Stuart about a lot of the things we talk about here. He was saying that the bottom has pretty much fallen out of the 'second hand' horn market unless it's collectable or vintage. There was a woman in the shop at the time selling an Armstrong 60's alto and had left there 4 years ago. She'd come to pick it up as it hadn't sold. Partly due to that fact that she was asking ?400. After she'd gone, we all agreed that we'd seen those go for about ?80 on Ebay.
Ebay has single handedly destroyed the shop trade for 'cheaper' horns, and many traders won't touch them as trade-ins for that same reason. When you can buy a brand new and credible Chinese sax for about ?100, who would bother having an old one re-padded for ?200?.
The best deal you'll probably get is to leave it at a shop and get them to sell on commission. Even then, you'll be up against Ebay. You could also try 'OTHER' auction sites on the net, adverts in your local paper, or sadly... setting your selling price low.
In the last few years the whole market has changed.