I normally price things by the job instead of by the hour. However with weeding I not take the slightest loss on that type of work. I will offer weekly weeding at whatever time is needed to keep the beds weed free. I will suggest that they start with of 30 minutes a week for $30. Once the weeds are under control, and or it needs less time then I will cut back the time and charge less. Though I have found that people do not want to pay to have beds weeded. Even when all it would take is $10 a week. They tend to only consider paying after the weeds have gotten so out of hand that they do not want to do it themselves. Thus it winds up costing a lot more.