As the boot floor isn't structural it doesn't need to be welded in place so rivets are a viable DIY option. There's still a lot of dismantling, cleaning, painting and drilling to do but nothing too difficult. It does need a lot of rivets and using an air riveter makes it so much easier.
There are a few articles on it and here's just one of them:
http://overland-rovers.com/ralphs-pages/repairs-and-ongoing-maintenance/182-boot-floor-replacement.html
Another advantage of doing it yourself is, as you'll see in the article, having the old floor out gives you good access to those areas normally hidden from view permitting you to de-rust and paint everything before it gets hidden again - something a welder probably wouldn't do.
Cheers,
John