find out more about garages that do the conversions
You may need some extra research before making this decission, because a few months ago there was a big fuss about a new tax on gas (LPG), which would put it's price too close to thepetrol prices.
Owners of garages doing conversions were complaining that they were losing clients very fast, because after some basic calculations the new prices made the conversion a bad deal, you wouldn't be able to earn much on the petrol/LPG price difference, so the costs of conversion would make the whole thing not worth it.
But I'm not sure if that new tax has been really introduced (or is going to be soon), or maybe not. Besides petrol prices are also increasing, so maybe it's still worth to use LPG even with the new tax?