JohnnyBravo fits them, but you are talking about a grand+ for the ones he does.

Single point injection kits are cheaper, like i have on my mondeo, but best way really would probably be to do what i did and buy a secondhand car with a kit already fitted.

Economy is worse on mine by about 1/3 than on petrol.
I get 37mpg on petrol, and 25mpg on LPG

But the fact lpg is less than half the price means its more like 55mpg equivalent cost