Thank you everyone for your quick replies and good ideas. I unfortunately got swamped with work and was not able to follow up until this morning...
Yeah, I agree that finding a replacement door is the best solution. The rust is barely noticeable now, so I have time to do a proper search--a year or two at least I figure. There are few decent wreckers in the area so I may have to go further afield--if anyone has any good suggestions in Western Canada, let me know!
When I received the detailed estimate from the Toyota body shop (technically, it's not Toyota as they serve all the dealer brands that are linked to the local Toyota dealer) was to replace the door shell with a refurbed shell, paint it, and replace some of the seals, etc., and reuse other stuff. Other than painting, I probably could do that myself. They were actually quite decent about it and said I should talk to another body shop who do good work and could likely do it for cheaper.
One thing that puzzles me is that they want to take off the front bumper and fender to do the work. I wonder if this is to better blend the paint? I guess if I want a good match on a used door I need one that's been on a vehicle that was parked outside continuously since purchase in hot summers and cold winters
Thanks again, folks. Very helpful information.