Probably a little more pricey. Here's a link to a kit from Kaemna in Germany with the 924 conversion listed at 1,380 Euros.
http://www.kaemna.de/cms_en/katalog....seite&seite=78 I like the theory behind big bore engines though...keep the revvy nature of the 749 with a good deal more grunt.
Whether it's worth doing is a different matter, I would have thought that the price of doing it once the costs of all the sundry items, labour and setup time had been added you'd be better off part exchanging for a 999