My Dad used to have a 68 Mustang - when he was looking to buy that he looked at various options like importing and converting. From memory, a pretty poor job then cost about 5 or 6 grand (parts and labour - but that was more than ten years ago) - and on a 60's American car it was relatively easy. I know for later models (i.e. 1990's) it could cost $15k to get a properly engineered, reasonably decent finish. If you were to throw in things like airbags, I'd imagine getting yourself a fully working LHD to RHD conversion would become nightmarishly expensive...