if you have a good garage and can weld well, it is probably viable if you have 3 or 4 months+ of spare time to give it.
Front wings can be fiddly to get right for gaps etc, especially if you buy pattern ones.

earlier in the year I stripped my mk3 and repaired the battery tray, fuse box base, and both front footwell to arch pieces, along with the leading end of the inner sills. Also had to remove off side outer wing to repair the front end of the sill and the aerial mounting plate.

It took me 6 weeks of full weekends as I had to fabricate a lot of the repair sections.

Bear in mind that you will always end up cutting out twice as much as looks rusty before you get back to weldable metal, and if the drivers footwell has gone, odds on the fuse box..hence loom, will have to come out to do a decent repair.

Satisfying work if you can do it, and although mine is not completed yet (wing needs professionally spraying), it is good to know I have saved it.
If you can't weld, I'd guess the work you describe would cost approx £1500 labour, less if you have a mate who can do it

HTH
Ant