Northney marina at the top of Chichester/Langstone harbours may be worth a look.
I use it just to slip as the boat is kept 4 miles away in my garden.
April - October £120/m = £702 (£58.50/month) includes slip use.
Can be busy at peak times but most users friendly and will help if solo etc, but if you plan you times it is not too much of a problem. Easy access from M27. I do Gloucester in about 2 hours from home, unless Crickley Hill to Birdlip is solid!!!!
The slip has access at all states of the tide, and you can escape under Langstone bridge from 1/2 tide ish otherwise via Chichester entrance at all times.
It is a bit out of the way for the solent but you also have both harbours to explore.
Cowes is about 20 mins via Langstone (at 25-30kts)