Still overpriced. Terrys signature doesn't actually add much monetary value to the value of a book, especially the earlier ones, because he has signed so many.
For instance there must be more signed early books than unsigned ones because people kept fetching them to signings and there weren't very many printed anyway.
Yes they are only worth what a buyer is willing to pay for them,I have seen a non Discworld book that I need to complete my collection but I'm not willing to pay the asked price as I think it's too much.
He willnae tak' a drink! I think he's deid! , on the other hand though A Midgie in yir hand is worth twa up yir kilt.
On what though. £40 is high for most of the later books even as first editions. Footnotes or the original hardback Eric can go for over £300. An original Colour of Magic would be about £6,500