The smallest I've been able to get things without completely breaking everything was around 230mb. This required lots of ugly hacks such as post install triggers that would remove useless garbage such as /usr/share/doc/ and man pages.
# debootstrap stable mydir
# chroot mydir apt-get remove -y vim-common nano netcat-traditional e2fsprogs
# chroot mydir apt-get clean
# du -sh mydir
228M mydir