The "poor man's" isolation transformer can be made by stacking two high-current transformers back-to back. Years ago, I made one with two 50V transformers I got from old 48V telephone system supplies. I just wired the secondaries together, and used the primaries as in and out. Mine was probably good for only a few hundred VA.
Here's a cool youtube video describing the same:
http://www.youtube.com/watch?v=QDSmv9E5VgQ
Cheers,