I showed a handyman who’s good at electoral work a light fixture and asked him to replace it with a fan. At first he said no problem, but later he thought about it and said it would be a much bigger job (has to cut open part of the ceiling around fixture, etc.) Not sure what he was talking about but he wants 0 just for the labor. Wonder if I’m getting ripped off.

First, a ceiling fan is a great deal heavier than the average light fixture -and so needs solid support. And it shakes and vibrates while in use, so not only does that support have to be solid but also resistant to shaking (not necessarily the same thing). So, if the existing fixture is not properly supported then a new hanger will have to go in – no small thing.
As to cutting away part of the ceiling – that would depend on several conditions, but if he is correct in that need and he cannot use an ‘old-work’ hanger safely, $100 is pretty inexpensive as it might well be a few hours work in addition to having to repair the ceiling. I know it takes me about an hour or a bit more to install a ceiling fan *with* the proper support already in place what with assembly and balancing. Installing even an old-work hanger for safe support adds another hour to the job – so you can see it adding up.
Only £50 to fit a ceiling fan? That’s REALLY cheap. It should be more in the £500. And ofcourse you can’t just fit a ceiling fan in place of a light fixture they take much more electricity and are much heavier.
I installed three ceiling fans in our house that did not already have a proper electrical box. Two of them were a piece of cake. I used a Space Bar. If memory serves correctly that’s the brand name. The third one I ran into a problem. It seems that there was a second ceiling above the lower one and it was difficult to fit the bar in place without cutting a fairly large hole, then patching after the bar was in place.
Code requires an approved hanger for any ceiling fan.
Yes. We replaced our central ceiling light with a fan only. See this site for detailed instructions. Most important when doing yourself is turning off main electricity and making secure electrical connections.
See this site for detailed instructions. To me it seems expensive for the labor, when in most ceiling fan situations an experienced person will be finished in less than a half hour.
http://www.lowes.com/lowes/lkn?action=howTo&p=Improve/InstallCeilingFan.html#3