that's a common place for them to rot - the rear beam will probably need replacing as well. To be honest, if it's that badly gone there will probably be rot around the front jacking points and other areas...the rot was pretty bad on my '95 QV which was why i got rid.
I'd move on to be honest - you'll be able to get a good one for the same price as you'll end up spending on that one unless you're keen to get busy with the welding torch yourself
Suppose if everything else is good it might be worth the hassle but i'm personally scared of rusty cars....