Hi...
We have a cast iron log burner and find it to be very efficient.
Here and here are a couple of links to suppliers. The first company have a wealth of information which they are only to happy to share with prospective customers.
We installed ours ourselves; we bought the unit from a local ferretaria, although similar items are available from AKI or Brico Depot or Leroy Merlin.
It is necessary to install a full length flue pipe from the unit to a point about 6 feet above the existing chimney pot. Once the flue pipe is installed fully the rest of the space surrounding the chimney top can be sealed off, thus preventing draughts coming down the outside of the flue pipe. It is a good idea to install a cowl to the top of the flue pipe; various types are available.
Additional ventilation for the room in which the stove is fitted is essential, especially after the original chimney has been sealed off...
As I recall we spent about 375€ for the unit itself and spent another 70€ or so on flue pipes.
Logs can be quite expensive however, unless you have a source locally; we have found it cheaper to run electric oil filled radiators in the living room and use 400W Ecoheat panels in the bedrooms.
Anyway I hope this helps....
fb