Interesting to hear that re filling speed, I'd just assumed it was a thing with all of them as it's the only vehicle I've had with LPG. It was converted prior to us owning it by an outfit near london for the cost of 1K, so you'd have hoped it was right for that.
Probably should have sniffed out more stations really, suppose we were just spoilt having one on our doorstep previously!
£1k is an OK price depending on the car. Back in the day, I used to charge £1.2-1.5k for converting most cars, with most towards the lower end of that and that was over 10 years ago!
As said, the pipework and the type of filling valve make a big difference to the filling speed.
My Mondeo had a 65 litre tank. That would take around 5 mins to fill up. I remember one chap at our filling station with a 307. It must have taken him 15 mins at least to fill his tank!
Another Mondeo of ours which we bought converted had a Stako tank, which had multiple fillers into the tank to assist the filling speed.
But even price doesn't make for a good conversion. It's hard to know who can convert them right. We managed to do them right, but we did take our time. IIRC, it was around a week we took on and off to convert a car, but we never wanted to see the car again (i.e we wanted it to work).