I'm wondering whether you've checked out the various web interfaces that purport to do this, and if so, why you decided against them.

http://www.ohloh.net/p/SVNAdmin

http://svnmanager.sourceforge.net/

http://www.google.com/search?btnG=1&pws=0&q=subversion+web+admin

http://insurrection.tigris.org/

http://csd.informatik.uni-oldenburg.de/~hoenicke/svnadmin/

This isn't really meant to be a "can you use google" mail as much as a "if you evaluated these, please share" one.