How much is appropriate to charge for maintenance/update of a website?

[Leanne]

I currently maintain and update a local companies website as an employee on the side of my actual job description, but am hoping to continue this maintenance on a freelance basis as I will be employed elsewhere. On average I spend 6+ hrs/week. How much should I be charging hourly or monthly for this service? I am also creating eblasts from scratch every other week (sometimes more frequently) as well as contributing graphics, photos, copy and marketing strategies along with updating facebook/twitter pages about twice a week. Keep in mind that I don't have experience professionally as a website developer.