All of the communities I've operated over the years have had loyal members that wanted to donate to the forum. I always wanted have the ability to reward members that donated to the forum in return for their support. Xenforo makes it easy to do just that.
Xenforo has account upgrade, or subscription, capability right out of the box. All you have to do is create a special usergroup with extra privileges like file uploads, the option to not display ads or even the permission to advertise in certain areas on your site to your traffic. When a members purchases that upgrade, add them to the new special usergroup and they are then granted extra privileges. After the upgrade period expires they will more than likely donate again to renew their upgrade.
Not only do upgrades bring in cash, they also make more loyal members that are more likely to visit more often because they have made an investment in your site.
You can have as many different upgrade packages as you want offering different privileges to your members, you are only limited by your imagination and creativity.
With Xenforo's user friendly interface and the core subscription system, you can easily make more than enough to pay your hosting costs.