I have an expat friend who had his Saab converted locally. The garage quoted him 1000lvs, at which point I warned him that for 1000lvs he would get a bodgit job.
Still, the saving was too much for him and he went ahead.
They converted it, not as a dual fuel but straight LPG , so this winter it has not started more than it has. I refuse to travel in it as currently, and he's quite proud of this, it only has SEVEN leaks.......And he smokes in the car.
It has been back to the garage more times than out.
As Owain pointed out it is quite a competative market, but good workmanship and reliability and you should make a good living.
A friend of mine in the UK started up on LPG conversions and he's just in the first 6 months won a contract from a council to convert 150 transit vans.....