Sounds like it has been abused. If the owner couldn't even be bothered to protect the interior after damaging the screen it doesn't bode well.
Replacing the rear screen and parcel shelf carpet is no big deal, about £100 would cover that. If it's been left open to the elements so long that the engine cover needs replacing I would be worried that water had got under the T-bar and run down to the floor pan behind the seats. So there could be corrosion, mold on the carpets, in the underlay, mold spots inside the hood ....
Impossible to put a price on it without a lot more details
MOT?
Mileage?
Tax?
Service history?
Condition of engine, lack of care for the car means those coolant levels may not have been checked regularly?
Coolant and oil, any contamination?
How long has the car been laid up, the longer it's been standing the more I would worry, the F is a car that doesn't do well sitting idle outside for long periods.
Condition of bodywork (dents, rust), in particular the sills near the rear arches (MOT failure if corroded), headlights (milky?), tyres, exhaust, underside, etc.
At this time of year there are lots of people selling F's and TF's which have been cared for and plenty of F's can be had for around the £500 - £750 mark in very good order.
Don't get too sentimental about an old F. Many people seriously underestimate the cost, time and effort needed to bringing a shed back up to decent condition and too many owners seriously over estimate the sale asking price of these cars.
Apologies for the long reply, it looks quite depressing reading it back now
Thanks for letting us know about it, could be well worth a look if you're local.