Cheapest genuine 19" Prets on Ebay are between £1500-2500 unless you want damaged ones. But considering all the issues with them cracking, you'd want to getting some mint ones.
Think CM wheels are definitely worth a try as huge savings.
They have 19" Reifntz in Satin Gunmetal for £500! Also, they have the 18" Prets or 19" Seville (black with polished red lip) for £500 as well which I've never personally liked in the factory grey but these do look good in this spec.