I followed that line of thought with Admirable Bird, we were out of town over night and the power went off. The temperature in the enclosed porch dropped down to the 30's and I lost A Bird two days later. Perhaps if he had been acclimated to cooler weather it may have made a difference. If you have a zoo in your area you may want to contact them about best winter housing for your birds.
There has been quite a bit of breeding since budgies came from the wild, so maybe you can talk with your local pet store and see if they can give you contact info for a local breeder.
