Use tips for that.

What can be of major value of one user, saving many hours and accelerating growth, can be just a minor adjustment for someone else. Furthermore, one user is investing hours and hours without any return soon, while others are cashing in and just need to keep up with latest trends. We keep our ideas, analysis, implementations and evaluations free, though express the time spent and potential as price, yet with a 100% discount. However, we do hope our community appreciates the value we provide them and they help us grow too.

We could use donations, but those are too generic; we want to see a direct relation between value for the user and us. Plus, donations do not fit a for-profit organisation, yet setting a hard price doesn't give us information on perceived value and could scare off those who could benefit most. Community over profit.