Do yourself a favour... before getting ideas of 800 for a car and 1800 for insurance go and get a quote.
You dont have enough for the insurance - let alone both.
My brother is 18... £3300 tpft on any car you can think of between 1978 to 2008 and anything from 998 to 1298cc and any value from £500 to £5000 quid.
Parked on the drive, not the worst area in the world.
Yes you can get it cheaper by sticking your nan and her dog on as named driver and yes cheaper still if you are the named driver and your nans dog is the man driver.