Remember, you're not charging for time. You're charging for expertise. How long would it take these clients to learn to do it themselves? How much would they pay to alleviate that pain? Even if you can automate the whole process to complete in under a minute, your client might take weeks to get it right.
You've already learned what they never wish to learn themselves, even though they need that skill to get the job done. So your abilities are valuable to them. You just have to decide how valuable. R1400 might seem like a rip-off to you because it's so easy for you, but for a corporate client who maybe makes R1500 an hour from their work, it's a bargain.
So why not start somewhere in the middle, say R1000? Phone each customer and ask if they would be willing to pay that. If yes, good for you -- you might be making R5000 extra per month out of your hobby. If not, ask them what they would be willing to pay, get all the answers, average it out and come up with a final price (final as long as it covers your costs and doesn't fall below the sanity level).
Also, whether its a hobby to you or not, to your customers it's all business. So don't sell yourself short.
+1
Don't shoot yourself in the foot with this one like I did. I was a bit more detailed than the OP, had service agreements in place, charged per hour for work, worked on a retainer etc. Even with regular timesheets and managing their expectations on what can be done in what time, the "quick 5 minute" jobs (add/remove a page etc) wasn't as quick.
The client then refused to pay because it was "ridiculous" so I made a deal with them, the next time I do a "quick 5 minute" job for them, I'll get all of the information I need up front, do a quote, then once the quote was accepted, I will do the work with the added clause that if there is scope change, they will force more time (they didn't believe that a "small change" to their original request will incur more time... which is dependant on their db's etc etc but anyway). Quote accepted, work done (1 hour), report done/formatted. A month later they come back to me saying it's wrong and where is column XYZ. I told them that the original request was for ABC, and they agreed on it, involving XYZ would have made me give you a different time estimate as it incurs more time from my side.
I then fired my client for doing exactly what they've been doing all along and then refusing to pay for time spent.
//OT
Question for OP, if you don't mind me asking: How much do you charge for setup ? What does it entail ? I've been looking at making WP sites for small (like, really small) companies in my free time. Just so that they have an online presence. But I have no idea about how to go about this with charges and stuff. Never got around to doing it, but holiday month is coming up. Would be nice to make some pocket money.
Don't fall into that trap. But, maintenance, I'd say charge them 1 full day out of a month * 80% for retainer.
So if you want to make R30k a month doing this, it's R30 000 / 23 (work days in a month on average or how many days you'd like to work for that amount of money) / 8 (hours in the day you want to work) = rate per hour you charge. In this example it's close to R164 per hour.
R164 * 8 * 80% = R1050
If you get 23 clients, that means you're busy each day of the week for at least 8 hours and making R24k. Since most of the work would take you less than 8 hours to do, you can add on 23 MORE clients without sweating it. Chances are they would use all of their allotted time each month is small, those that do gets offset by the others that don't, and if it's a full fledged project you can still charge them per hour of R164 over and above their maintenance
*edit
Above excludes any costs you'll incur, for example, hosting. Once you delve into that realm, you'd be inundated with email issues and bull****, so prepare for that
