Pricing?

Hello! I recently finished this little animation (frame by frame) and multiple people have expressed that they would like to commission something like this.

Now, even though this is only a short, relatively simple loop it took me about 40 hours. I'm sure I'll get faster once I do more animating (this is like.. My 4th animation?) but I don't think I'll become any faster within the foreseeable future.

Now, I have no idea what I would charge for something like this. On one hand I don't wanna overprice it as it's still somewhat amateur-ish, on the other hand I don't wanna underprice it because it took me ages. Any ideas?