It's not bad in November Boxtops. We went across from Lymington to Yarmouth on November 7th about 4 years ago. We were just one of three cars on the WightLink ferry. It cost about £30 return I think.
A good way to get the cheapest prices on all routes is to use aferry.co.uk<a href="http://www.aferry.co.uk>Isle of Wight Ferry</a>. They have a really good comparison service.