What is a reasonable rate for a web designer to keep a site updated (e.g. adding new content, pages)?

Do webmasters charge by the job? The hour? In 15 minutes increments?

Any advice would be greatly appreciated.

about 60-100 an hour. some charge just like 400-1000 for the whole job. but updating , id say maybe 60 an hour

I have a maintnence agreement with my clients after the site is up and running. It's $50 a month for hosting, some SEO & up to 3 hours of updates, after 3 hours it's $40 an hour. I haven't had any updates take me more than 3 hours a month yet.

I currently charge $40/hour for any work. But when it comes to updates, I offer a deal that if they prepay for 8 hours of work, I'll only charge them for 6.

And updates are done after 5pm or on downtime.

-Line