You need friends who have the right equipment and it's quick and easy. To guillotine the spine off. Ask the local printer to do it as a favor. They'd be pretty tight if they asked you to pay for one cut. Find someone who has a auto feed scanner that duplexes like the one we have at work which emails the scan to you. It will scan each page in about a second.
With 400 pages you'll need to use Elfwreck's binding method but if smaller perhaps someone you know has a hot glue binder at work with clear covers and you can bind it back up.