Northney was £20 last time I paid but it is often unattended so you may get away with it ! They have a good car park which sometimes has a barrier lowered late in the day but they monitor on cctv and will open up if you have paid .
Chichester harbour will charge you for a day ticket if you are spotted best to buy an annual which is shown here http://www.conservancy.co.uk/page/Ha...s-Charges/319/
Call 'CHI HARBOUR PATROL' on 14 you can pay on the water if they are around .
There is a speed limit of 8 knots all the way from Northney to the Bar area , it is enforced !
Langstone harbour also has a limit but not sure how rigorously they patrol it .
Both harbours are interesting to enter in wind against tide situations.
Chimet is a good source of weather / water conditions . If returning to Chichester entrance keep well offshore to avoid Winner sand south of the island and don't be tempted to cut the corner before West Pole it gets quite shallow and big waves build up even at high tide .
You can always stop off at Hayling Sailing Club for a pint and the best Sunday lunch in the area .