Although the content is provided for free by an enormous number of volunteers, there are technological and management costs.  The wikipedia page provides a link for one time donations, but there is a hidden option to contribute a monthly or yearly amount automatically.  I don’t have the faintest idea why this isn’t made more obvious (I haven’t found any wikipedia pages linking to it), but if you can’t contribute a whole lot of money at one time, here’s the way to make some money drip wikipedia’s way, little by little.