You know the small indicator on the side wing.How much would it cost to get a new cover for one and has it to be fitted by the dealer?

no they normally pop on an off, your talking about £20 but maybe you can find one on ebay have a look!

Try the local scrapyard or car breakers mate.
They might have a 2003 Megane in the yard for breaking (Accident write off or something like that), so long as the side indicator cover is intact, u will drive away with it for £5 at most, pop the old one off with a fine flat blade (carefully) & press the new one into place until it clicks my friend.

My advice would be to get the scrapyard dealer to remove it from the car in his yard & watch how he does it.

Hope u get sorted out soon

Regards

Gaz