I look after a domain registered in my mother-in-laws name, and I've deployed Joomla to the site. She sends me weekly changes (job postings, changes to existing articles etc...) and I make the changes within a few days. The site is for a business, so she wants me to be able to invoice her for the work, but I don't know what the going rate is.
What would people feel is a sensible amount to charge for such changes? They only take in the region of 15-20mins of my time a week, so it's not like I'm spending all weekend updating the site. Would you charge per change, or an annual fee?