Depends on condition or whether it is a genuine white or red frame model. I would guess £400 for a knacker up to £1300 for a minter.
Excellent bike if you get a good one.
I have one, love it, I am a bit selective as to which trials i go to on it.The problem as Tim says is you have to compete against the modern stuff as its a mono. there are the odd classes for air cooled monos but not many. As a rule I ride one route down from what I would ride a modern bike in.
TY mono
brill bike had mine for years ride it wash it ride it again about £800.00 will get you a good one and you get the added pleasure of beating people who have paid three times as much lots of clubs run air cooled classes and if your only doing the easy routes shes more than enough with trials bikes its not what you ride its the way that you ride it