I have the interior out of my 1972 Spider to put in heat/sound insulation and new carpets. Everything was going well until I took out the map pockets and found the rust. I noted some body flex and wrote about it before (http://fiatspider.com/f08/viewtopic.php?f=30&t=15874). In short, when the car is on jack stands at the appropriate points, the doors rub very bad. But on the wheels, it is fine.
Here are some pics.

Driver's side. Note the rust in the corner.

Driver's side close up

Passenger side. Not as bad but rust higher up.

Passenger side close up.
So the questions are.......,
1) How bad is this? Is there a pre-fab patch that I can have welded in? Am I going to need to find a donor car to cut from? Can this be fixed from the inside? Or will the fenders need to come off?
2) How common is this? Should everyone look out for this area? How can I prevent this from happening again?
3) How expensive is this? (ballpark)
4) Any recommendations in the Atlanta, GA area to take it to? I would like someone that has been through Fiats before.
I am good at fixing mechanical problems but do not have much experience with welding/body repair. I went ahead and painted these areas with some rust preventative paint. It made me feel a little better. I was hoping to get this car on the road very soon but I know this must be fixed before I go any further with my interior.
Any ideas, suggestions (and comfort. ha ha) would be appreciated.
Thanks,
Dougieb