Didn't you already make a thread identical to this one recently? If you're not getting replies, reposting the same thread is not a good way to remedy that, it just makes you look bad. On a related note, the frequency with which you bump your portfolio thread is also rather off-putting, you might want to space your bumps out a little more. Bumping frequently makes you look desperate, which in turn just looks like nobody wants to work with you, and whether that's true or not, that's not an image you want to project.

Price your work by how long it takes you to do it. The hourly wage could be anything from US$10 to hundreds of dollars. Below $10, you're just devaluing yourself and all other artists. $10 is what you would expect to charge if you're slow or can only do very basic work, hundreds of dollars is what you can charge if you're fast and you have multiple clients vying for your limited time. I realize that's a very wide window and isn't helpful. Maybe aim for $20 as a base wage, and tweak it up/down depending on how difficult you expect the work to be? If you have to ask about prices, I assume you're not getting much work, so starting on the lower end of the pay scale is a good idea.

Another factor is the project's budget. The same artist might get paid very different amounts for the same amount and quality of work just depending on the project and its budget. For this reason, it might not be a great idea to have fixed prices listed, especially if you're open to working with smaller devs with shoestring budgets.

Lastly, price yourself by the sprite/animation only if you expect to be working by the sprite. Usually, artists are brought on to do more than a sprite or two. Devs want to know how much they can expect to need to pay you to get all the work done that they need. For this, an hourly wage along with completion time estimates are much more useful than "I will make you a sprite like this for $50."