I have a couple of components on Purity 3 that are built using BS 2.3 and there is a simple (and free) way to do it if you follow the advice this Joostrap blog http://www.joostrap.com/support/tutorials-videos/206-boostrap2-to-bootstrap3-super-easy-update
You need to install NoNumber Replacer and copy/paste the Search Box/Replace Box entries to make it work.
If I understand the process correctly, it searches for the BS 2.3 classes and replaces them with BS3 classes whenever it finds any.
When I used it the BS2.3 components worked with only 1 or 2 minor css adjustments for layout.
Hope this helps.
Note: Just a thought ref ITPrism for crowdfunding, the product is fine but I tried it as well as JGive and found JGive to be a much simpler option and as a bonus it integrated with EasySocial. JGive uses BS2.3 and required the NoNumber conversion. Obviously you should use what is best for your requirements. 🙂