alternative to wp-signup process

Have endlessly searched, but this is a difficult one as there aren't a lot of common search terms. SO, what I'm hoping is that a multisite guru will know the answer to this...

How to allows users to create sites on the front end without modifying wp-signup or paying Gravity Forms $200 a year for the privilege.

I cannot modify my wp-signup page for some unknown reason and have been unable to locate a plugin that does this. Ideally this should be a front end option, but can't find a plugin for it.

REALLY WISH that WP would allow direct customization of their registration forms ("gimme a site"? really? what are we, four year olds here?) but until then...?