Hello Mel,
Generally the cost of living is the same as mainland GB as we have the usual run of supermarkets such as M&S, Morrisons, Sainsburys, Tesco, Co OP, Lidl, Aldi and Asda are just about to start building one of their supermarkets very soon.
The problems come when you want something from the mainland and then you run into the cost of delivery or the fact that some retailers just refuse to deliver.
I have on a lot of occasions had to have items delivered to Red Funnel at Southampton and then pay for them to bring it over on the boat and pick up at East Cowes.
There are a lot of people who visit in the summer months and fall in love with the place and decide to move here just to find that in winter it can be a very lonely place as most things apart from the main shops shut down for winter and they find the fact that they are cut off from the mainland on quite a few days due to weather, and of course availability of ferry places and the extortionate cost of the ferry crossings.
When we take the van over to the mainland it costs us around £180 return, and that is money spent going nowhere, sitting on a boat for 30 minutes !!!
You very rarely can just decide on the spur of the moment to go away, like for instance when the music festivals are on, there simply are no spaces available for a week.
The nearest decent theatre is the Mayflower in Southampton and again you have to consider the boat timings if you want to go and see a show, or spend a night in a hotel.
On the good side, if you want countryside to walk in , there is plenty.
There are some beautiful sandy beaches which are dog friendly from the end of September to beginning of May but then become no go areas for dogs, which is fine.
There is one place which is dog friendly all year and in my opinion is the very best place for dogs as there is a very large "dry " area to run around on and over a sand dune is the "wet" side where the water is very shallow and very sandy. The council tried to ban dogs during the summer but local opposition won and they withdrew the idea !!!!
Crime is on the low side and generally involves nuisance damage to cars, or domestic disputes.
Really violent crime is quite rare as is vehicle theft, or caravan theft (mainly as there is nowhere to run to as they stop the boats if a vehicle is stolen)
Housing I think is slightly lower than the mainland, but not by much, and we have a very high population of elderly folk so pressure on local services is high, especially as we only have one hospital and getting a doctors appointment is a 3 week wait usually.
Driving is, or can be ,challenging as the normal rules of the road seem to be ignored by a lot of people, so always expect the unexpected as it WILL happen on a daily basis.