Lots of new single posters wanting to get rid of electrics lately.Why would you want to devalue the Calais by drilling non genuine holes inside the rear doors? Personally I'd just leave the rear windows permanently closed if I couldn't fix the motorized winder.
I've also had no problem getting rear window motors on ebay in the past year. Bit of a pain to change- you have to drill out and replace rivets etc, but doable.
Here's a tested and working RHR regulator for under $50 on Gumtree:
https://www.gumtree.com.au/s-ad/wet...gulator-holden-commodore-statesman/1272241893
The bloke also has a LHR regulator for the same price.
I'd pull the worm gear out of the replacement's motor and grease it with moly grease before I reinstalled it.