Sale have charged £10 for the car park for the last couple of seasons (added an extra £5 to pay for free shuttle buses to and from the TC) so maybe the stadium just quoted the wrong amount?
The pub now also charge £5 for carpark
on a match day, whether you buy anything or not, but that only started happening recently when they realised the price of the stadium carpark.
There is no legal requirement to provide disabled parking free, just a requirement that they can have the same access as other paying customers; until the start of Sale's season the stadium allowed this for free, but now appear to charge. The reason they gave is the restricted size of the car park now that the development sites around the stadium are in process of sale. The only CP attached to the stadium is the tarmaced one at the front. All the stoned areas are sites up for sale and development.