Pay what you want for them all. $10? $25? $100!? It's definitely for a good cause. You can chose how much you want to go to charity (Like The Electronic Frontier Foundation and the Child’s Play Charity) or how much you want to go to the developer. In this case all money that goes to Croteam will be used in the development of Serious Sam 4 coming in 2014. Also how much of a “tip” to give to the Humble Bundle team. The tip money goes towards keeping the site up and running.
Croteam also gave us a funny advertisement video about the humble bundle sale as well as a “tease” for Serious Sam 4. So far 73,460 copies (as of 12:37 AM June 8th 2013) of this week's bundle have been sold. A total of $315,644.65 has been raised so far with the top three contributors consisting of $151.00 $180.00 and $200.00. I am thoroughly impressed and proud of these three.