VAUXHALL Insignia Mk1 (A) Hatchback (G09) 2.0 CDTI (68) 160 hp

Hi all...New to the group today as I'm trying my best to help my 80 year old Father in law out after he has been ripped off by a garage.
Basically his N/S front headlight is fogged up and light is flickering.
The garage replaced the Ballast and bulb and apparently tried to re seal the unit....3 weeks later he still has the issue!
Took it back to the garage yesterday and they are now saying he needs to buy a whole unit! He had paid them £548 for that work!! ( Don't worry I got a full refund from them today)
My question is How do I find the cheapest complete headlight,I'm more than capable of fitting it myself but there seems to be lots of different versions!?
His has the Xenon bulbs in it if that helps.
Hopefully someone has had a similar issue and can point me in the right direction where to find the correct part to get him up and running again.

Many thanks.