£3k would buy you a lot of work
£4-6k would buy a 10-valver that needed slight tidying.
£6 - 10k would buy a very very good / mint 10 -valver.
£20k would buy a mint 20-valver from someone who wanted every last penny from the sale.
These prices , like all classics, do vary.
It is a minefield......if you really fancy one get on the owners forum and see what the pro's and cons are and what to look for.
Then see the bank manager and insert smile on face.