Mapquest.com.
Select you starting and ending points, give your MPG (or kilometres, whatever.) and it will tell you the cost. (Though you may have to convert it to MPG before giving it to the mapquest thing.
I drove from Newcastle Upon Tyne, to Aylesbury, in a 2 litre focus zetec climate. It was about £70 ish. You would have to alter slightly for the distance changes, but with a 1.1 it should be cheaper.... I would say about £60. Max
Indeed. Depends where you buy your petrol from in Brighton.
Personally when I'm down Brighton way, I find the cheapest petrol station is on the A23/A27 roundabout, just outside Preston Park.
As for the amount you'll need. If you take the direct route which is M23, M25, M40 to Birmingham and then the M6, you could probably do it on a full tank. Then you'd need to fill up again in Manchester. Your probably looking at £60.