We've been trying to answer the same question. We found that giving a free option forever has worked best for us so far. Free to start and free to use as your company grows.
For Gemba, this could mean limiting the number of connected Git repositories. I decided against this because:
(1) some new users try out Gemba with a test repository, and needing to remove it to free up a slot for the "real" repo seems like unnecessary friction;
(2) some designers work full-time on a single product (e.g. in a startup) and would get loads of value (pushing hundreds of assets) for free and might never need to unlock unlimited repos.
Sigh... I wish I had seen this about 2 years ago. Not so useful for me anymore since moving away from native app development, but that graphic of the manual QA process made me groan.
Great story and all, but please add some navigation links to your blog post template. I had to open a new window and type in your URL (http://gemba.io for those reading these comments) to learn what your product really does. The tag line certainly grabs attention, but at least link the logo/text in the header to your top level page.
http://www.thesnaffu.com