I don't do sprites myself but I know that sprites take time and effort. And I personally see a problem with how low your prices are.
I understand that you're new here, so I also understand that you don't yet have a good feel for what constitutes a... decent wage, shall we say. So let me try to put that into a bit of perspective.
You have a grand total of 13 posts as of this reply. A VERY grand total, isn't it?
At the same time, you have amassed 140 reborn rupees. If you were to buy commissions from yourself at a R5-20 per commission rate, you'd have between 7 and 28 commissions queued up. That quite a lot of time and effort that you've committed yourself to, isn't it?
And so I'm glad to see you have a 5 queue limit. But I feel you're selling your time quite short of a reasonable mark.
If ever you run low on 'work' you could always have sales, giveaways, or ask members to come up with challenges or ideas. Certainly, it may be to your advantage to charge less for commissions if you were to use it as an example of your craftmanship... Grand Opening Deals... Any number of commercial tactics may be used to keep yourself suitably occupied and/or challenged.
Far be it from me to tell you precisely what to do or how to value your work, but it occurs to me that time spent working on fulfilling this commitment is also time not spent exploring other topics, discussions, and possible connections with other members within the forums. I've been here a long time, and not without reason. I assume also that you enjoy your work, or you would not offer these services. And so this is but a bit of friendly advisement.
And that is why I suggest adjusting the pricing to be higher than it currently stands. But that is up to you.