Having said that, if you do anything for money, it is quite easy to become corrupt. Take google for example, they used to say things such as "don't be evil" etc. But, since they are a for profit business, it is just pure talk.
The point is, knowledge and health cannot be and should not be offered for the exchange of money. if you truly believe in your mission, keep the good work and request people to donate. If your work is really good, you will never have trouble with your expenses.