Secondhand, yes, in comparison with a RHD equivalent in the UK. But LHD cars are now increasingly expensive in the UK.
<<<If I buy one in another country is it easy to register it in France? >>>
Depends. If its a mainstream late model then you're less likely to encounter problems with the ever-helpful, smiling presence which is the french fonctionnaire. If there is anything non-standard about it then you are maybe in for a long haul.
It helps if you have all the original documentation with the car, especially the Certificate of Conformity.