WrapBootstrap is a platform which is already around since 2012. Theme designers and developers can sell their own creations based on Bootstrap on this site. There are a lot of themes available ranging in prices from 8 to 104 Dollars. Often the authors are doing sale campaigns where they lower their prices for a certain amount of time.
Especially Themes for admin dashboards or web apps seem to be very popular on this site as these themes have the highest sell rate.
Like on many other sites too you can filter all available themes by categories like business, creative, retail, restaurants, travel, food and many more.
Most themes keep being updated by the authors. If you want to get an impression about the theme creators you can take a look into the comments section of each theme. People are able to ask questions there and usually the theme authors are responding to them, which is a good sign