Go and find out what kit they are fitting and if single point or sequential multi point and let me know. I suspect at that price it will be single point with a vaporiser on the induction side rather than individual injectors in the manifold. Nothing wrong with single point, just a slight drop in mpg from my experience. To give you an idea our van does 18mpg round town on petrol but 16mpg on gas, of course the cheaper fuel offsets that easily and the price difference on our van was £1000 for the single point and £1800 for the sequential multi point.
Ours was fitted by these guys,
http://www.ozonlpg.com/ bit far out but they are highly recommended
If you are going to DIY buy the Iwema
http://www.iwemalpg.com/, best bit of DIY kit in my experience and comes with a certificate to show the insurers if needed (though in all the years I have used multi fuel vehicles I have never been asked once).
