How much is 1984/5 Ridgeback STD mountain bike worth?

[Ideale]

A friend has one with the original receipt-2 careful lady owners!19” size.
She’s looking to sell it with my help. And from what I can see there aren’t many of these around.It’s all original spec inc tyres.I will be able to get some photos in due course.
Any ideas re asking price?
Thanks

 

[Ideale]

Any ideas ?