#1309
If you look on bookfinder.com there are signed first editions on offer for between approx £15 and £30 and there is actually one on offer on Ebay for £15. The first edition was published by Little Brown in 1997, however, I'm pretty sure, Little Brown use a number line to indicate which edition it is so it doesn't sound like you've got a first. Yours could be a book club edition who's the publisher?

Personally if it's not a first I would start at £4.99 depending on condition and see what happens. I'd probably start a first at £9.99.