In reply to andyd1970:
Depending on the miles you do, how long you're going to keep it, look at unpopular petrol models (so cheaper to buy) and LPG convert them. You can DIY if you're competent and do it v cheap.
I pay 65p a litre at the moment.
Although if it's a 4x4 with the spare on the tailgate you probably need to fit a new petrol tank.