The cheapest and closest car park is The Quay/Cathedral carpark. Park on
level 4 or 6 and walk out the northern side and through the dragon tunnel
under the inner by pass and follow the road beside the White Hart until you
see Spectrum opposite at the pelican crossing.
Magdalen Street car park is at the bottom of South Street opposite the Southgate
hotel. Its slightly dearer than the Quay/Cathedral car park, but both
are much cheaper than the Guildhall and Mary Arches car parks.