You should be able to get your engine converted to LPG and a tank and external filler fitted to your van, for well under £1k. Just work out how long it would take to make up that outlay, then after that you're in profit
![Wink ;)](http://www.cleanitup.co.uk/smf/Smileys/classic/wink.gif)
Performance is virtually unaffected, you lose approx 2% horsepower off your engine which is nothing. Just need an engine which is suitable for LPG. Oh and check how many petrol stations in your area serve LPG cos if there's none don't bother!