The value of a record depends on rarity and the artist involved. In this case the rarity value is pretty obvious - there would be a handful of acetates run off from any recording session at most - and the artist has undergone something of a renaissance in recent years. Record Collector magazine is the place to look - you can submit letters asking for valuations...see
http://www.recordcollectormag.com/
[email protected] runs the official Davey Graham website - she'll be interested, certainly, and may be able tell to you more about the tracks.
http://www.geocities.com/davygraham/
Kay's site lists the tracks on Davey's first LP for Decca, issued in 1965. Do you recognise any of these titles? Leavin' Blues - Cocaine - Sally Free and Easy - Black is the Colour of my True Love's Hair - Rock Me Baby - Seven Gypsies - Ballad of the Sad Young Men - Moanin' - Skillet (Good and Greasy) - Ain't Nobody's Business what I do - Maajun - I Can't Keep from Crying Sometimes - Don't Think Twice, It's All Right - My Babe - Goin Down Slow - Better Git It In Your Soul