Are rotting floors the death knell? Help needed...

First off, I'm in Ontario, so I know exactly what you are talking about. Aside from the very odd, very, very low mileage example, these wagons are disappearing quickly! They are turning into piles of rust before our eyes. On almost any 18 year old car here, changing the fuel and brake lines, ALL of them, is standard operating procedure for me. I do the flex lines, too. Having had lines go, even on fairly low mileage cars, I don't take chances now. The floor is very much fixable. Unscrew the threshold plate in the door, and the carpet can be lifted up to inspect the floor from the inside. The expensive part of fixing the floor is the work of the shop doing the prep work. If you remove the seats and carpet yourself, and have it towed in, the shop can do the repair quickly and easily. Having a piece of floor welded in is not a big job at all at that point. Since it is not structural on these full framed cars, it is possible to pop rivet or screw a piece in, too. Just use POR or some other rust neutralizer after you cut out the rust pieces. I don't know if Lawrence is still in business in Prince Edward County, but he would have had it fixed in half no time. He likely had to close up when the County outlawed the yards. Minaker's had to close as well, which was a crying shame.

 

These cars seem to rot by the area at the lower cowl/ rocker panel and that corner of the floor. Brake lines on any GM of this age that didn't live in a dry climate is a given.
Fixing the floors properly is a fairly large undertaking but there are plenty of ways to patch it up in a practical manner.

 

Death knell, if it was a rare piece it would be worth fixing. I can buy cars like that all day in my area for a grand or less and at least one a week hits the local boneyards on average.
If the brake lines are shot the underbody and frame are probably rusty too. I'd rather pay a transport guy a grand to bring me a clean car from down south or out west than spend two grand trying to fix rust like that on a local car, why fight rust? The rust and rust repair never stops, it's the gift that keeps on giving and the only way to re-gift it is to sell the car.

 

I've written about my own 55 Chevy wagon having beer cans cut and riveted over holes near the kick panels below the windshield. Yes these are typical areas where often a rubber drain hose has rotted letting rain leak in. Also as someone else mentioned getting in and out with wet, muddy, snow covered boots is another source of moister.
Complete floors really can be replaced or patched. Those, rocker panels, and behind rear wheels are common areas for rust on any vehicle. If the wagon is otherwise nice go for it.
The mechanics and the price would be my big issues.
And it's just common practice to replace all hard and rubber flex brake lines. Rubber rots and steel rusts. Less than $200 in parts.

 

BlueVista: In Ontario, it is quite normal for the brake and fuel lines to rot long, long before the frame even starts to show weakness. If you are handy, it is not difficult to change all the steel and flex lines in a day in the backyard. To have them done is still not all that terrible, even with the labour being about $100 an hour around here. Say about $500 for all the lines that normally go. A reasonable, but not show quality fix for the floor is not a big job either. The body shops here are used to doing it. The biggest part of that job is removing the seats and what trim is necessary to peel back the carpet safely. Do that yourself, and floor repair is not difficult at all on these cars.