I agree with Pete. There is no reason why working with lime should be more expensive. However Pete may be overestimating the willingness of Irish tradesmen to try "new" methods (and believe me, lime work is indeed foreign to the vast majority of Irish plasterers and general builders). It's going to be up to you (or your trusted builder) to educate yourself on the value of lime vs concrete and to ram those beliefs home to the workmen you engage. The chances are that the workmen will not understand what you are asking them to understand, but that's OK in one sense, because the vast majority of them could not tell you the advantages of concrete (none that I can think of apart from strength, which is rarely needed) either.
Good luck with it. Been down that road myself, and ended up doing more of the work myself than I wanted to. Hope your experience is better.