Probably not true. If its truly cobbled together as described, and therefore a lot of it has been created 'key to disk', then most of it is probably unnecessary code. Replacing it with a rewrite would more than likely require code that is a considerable order of magnitude lighter than 200k (say between 50-100K). I've seen this kind of crap before a few times, and have succesfully replaced with rewrites, and in reasonable time frames. The main key to doing a rewrite succesfully however is NOT to look at, or replicate the code as it is (but just a bit tidier). The best approach is to go through a proper design to functional specification process, just as if it was a new application.
Doing it that way you'll probably find far more elegant coding solutions than are currently being used by the 200k mess and these will cut down on coding time. Moreover it will produce better and more maintainable code, more than you ever would through a tidy and document process. If you think about it, documenting what the spaghetti is doing would probably take as much time, if not much longer, than a fresh design/spec process. Basically the time taken to do a good rewrite is very rarely going to be longer than it would be to unpick the mess. Just keep your team very, very small and make sure everyone including your programmers are involved from the first design/spec discussions onwards. Things go much faster, and you get a far better design, if your coders are invested fully in the project.