@Amber Lynne: It depends. On Voltra I haven't really done a pricing thread or anything because I'm not sure what sort of work I'd be willing to do for digital currency. Usually I offer sketches on forum sites, since they're quick and easy and require little effort to make something that looks nice.
For the full-body commission style I've posted so many of, I generally base on about 15$ an hour (counting time spent actually drawing, and not the time spent faffing about and making myself drinks or getting distracted by podcasts and YouTube). I usually give an estimate of how long it'd take and thus what the cost would be after knowing what the person wants done.
I'm pretty fast when actually working, so like... The commission of Pied Piper and Trickster I just did in full color (with the full size psd file included in case changes need to be made later) ended up being 60$ for the two characters. Full color/inked bust or waist-up portraits usually don't end up more than 10-20$ for example. If it's inking and not coloring, it's even cheaper and faster. Those end up being about 10$ at most for a bust, 15 for a waist-up.
I don't actually like offering full-body color commissions, but this was a special occasion and the gift is for a fan of my comic/art, so I was a bit more lenient. x)
Sketches I usually charge about 5$ for busts/waist-ups, and 10$ for full body, just because I get them done so quickly it feels wrong to charge more. I'm not professionally trained and I don't have the Most Best Desired art style so I don't feel comfortable charging too much for any of my work, but I've been smacked around by artist friends often enough that I know better than to charge too little, either.