Both of mine have gone, I recently had a quote from a local garage who basically called Renault and Renault told them they couldn't be replaced, a new hub assembly would be needed on each side resulting in a quote of... £2,200+! lol
No way on earth I'm paying that when I know they CAN be replaced, just most places won't entertain the idea because it's so involving and there's a risk of damaging other things and having to replace them too while doing the work.
From what I've heard your best to pop the new ball joints in the freezer to contract the metal so they drop in easier, I would go steady on heating the hub up as it's aluminium. My mechanic who's an ex ford m-sport guy has said he'd done a few of these on the Clio before and he prefers to drill the old ones out so not to risk bending/distorting the aluminium using a press. Then with the new ones having shrunk down in the freezer overnight it only requires a little heat on the hub to drop the new ones in.