It's worth what anyone is prepared to pay for it, but if you go to:
which, in fact, is based quite close to where I live, you'll find a range of new and used laptop prices which should give you an idea in your case.
The price you should pay would be a little below the retail price of a used model.
The website involved also carries accessories, spare parts for many makes, does repairs and also stocks secondhand desktop systems.
My daughter acquired a secondhand Toshiba Satellite laptop from the firm and has been delighted with her purchase; it was a year old and half the new price and also had the balance of the Toshiba three year warranty remaining.