I was almost put off buying one, by the thought of body repairs (I have no skills and keep the car in a neighbours garage), but so far I haven't found them too expensive. I recently decided that, rather than put another patch on the floor around the peddle box, I'd get the front section of the drivers side floor replaced. I got a local body work specialist (a lot of his other work is on classic Ferraris and Jags) to put in a new floor section (£90 from alfaholics). He also replaced the outer and middle sills, on the drivers side and put alot of new metal in the rear wing (a previous restorer was a genius with filler). I told him there was no rush and he had the car around a month, but the total cost including painting (excluding floor panel) was £498. I had driven the car for 6 months with several patches of orange rust on the floor like those in your photos, I asked the specialist about these, he said to wire brush them off and then paint with primer, I did this in the open in a couple of days.
Once you get into driving an old Alfa (probably any other classic too) you feel like you've escaped the rat race, journeys aren't about getting there as fast as possible, other drivers usualy give you more respect, room and smile at you. Driving a Bertie I'd sum up with one word "Special".
Hope this Helps.