The value will depend on the mileage, condition, how well it's been looked after, whether it comes with an MoT etc. I would pay somewhere between £250 and £800, with the higher end of that pay scale reserved for a Clio in good nick that has low mileage for it's age, comes with an Mot, doesn't look like it's on it's last legs... What you don't want is the false economy of paying pennies for a car, and then almost immediately having to pay for new components.

You probably know to look for things like the condition of the tyres, rust, unusual engine noise (make sure you rev it), responsive brakes, steering (make sure the car doesn't pull in one direction, could be a sign the tyre alignment is out), gears (make sure these change easily) and the service history. But it's also a good idea to check the spare tyre (and make sure the locking wheel nut is there too), the air conditioning/heating, all lights, windows and signals, and the locks. Make sure you get the V5C registration document, you won't be able to tax the car without it, as well as all the keys. Check the paint and bodywork for signs of damage, it may have been in an accident if the paint looks uneven or there are strange gaps between the panels.

Obviously an 17-year-old car will have wear and tear, but make sure you know exactly what you're buying. Check the recorded mileage on the service records and MoT certificates, make sure it's consistent with the current mileage/condition of the car. Also check the MoT status and history online: www.gov.uk/check-mot-status