Any one hazard a guess...

No and no. Value is what a normal, sensible, reasonably knowledgable buyer will pay for something, not what a specfic individual would pay for it or what it actually sells for. (Unless of course the specific individual / sales price happens to be the same as what a normal, sensible, reasonably knowledgable buyer would have paid.)

I agree, but you can still get lucky with someone who has no idea/doesn't care what the sensible value is

that goes for sellers and buyers alike

i would guess at £200 but others may say higher or lower, i may get flamed for my estimation, but there you go

£200