Checked it out myself the other day, the slip is a good wide slip with a nearby pontoon for loading ect. Prices approx: £7 upto 100hp £14 over 100hp Parking £6.50 for car £6.50 for trailer. Max 20 hrs. So thats almost £30 for a launch. Plenty of room in car park during week, advise that it gets full early at weekends and can be congested with dinghy sailors. On street parking available for free in vicinity say 5 to 10 min walk.
Regarding Calshot last week end: I believe that over the weekend the winds were unusually (relatively) from the east / north east which would leave it exposed. The 'normal' wind is from SW from which the slip is sheltered.