how long did it take you to make that? It helps to factor in the amount of time you spend on your work.

well, your time is most important, so figure yourself an hourly rate you'd be comfortable with.
Lately I go with $20-$25/hour. So if I spend 4 hours on something then I would charge at least $80.
This is an art, and jobs can be few and far between(especially if you charge higher rates).. Usually if you charge higher, you'll be looking at finding serious work that appreciates the work and will pay for it, so you'll choose those jobs. If you're just doing a little task for someone or something like that, and there's no bigger plans for your work, then the compensation will be of a relative scale.
Look at the type of job it is, and the goals involved, and you'll get a better impression as to whether its a more costly project or something cheap.
If you lack experience, then you'll be more likely to find things that act as a stepping stone, so don't fret over it yet.
Perhaps you could ask for $60?

It pretty much depends on the customer as well. If it's a professional company you would charge way more than if it's a college student making a game project, for example.

As AlexHW said, it's good to have a minimum hourly rate (similar to how Elance works). Definitely, for the work you have shown us I'd have charged more than $30.

Anyway, keep up the good work and you will find nice and generous customers in the future :p.

I see, yeah I messed up setting the price, oh well. Next time..

Thanks! I prefer the cup to be half full, rather than half empty. Makes learning and life easier for me. haha