I thought I'd start a new topic for this.
I thought of an easy way to set monthly bandwidth quota limits. You can take any action when an user is over quota, but you can't limit his bandwidth. You don't need any apache modules to do this and it doesn't use to much cpu. I can get this done in a few days.
You could use mod_cband for more advanced options, but the developer's site has been down for a few months and it may be difficult to install it automatically.
What option do you think is better?