Can I really pick any price?

Yes. (within reason) Obviously, I'm not going to read an audiobook for $5. If you regularly order voiceovers, you know what going rates are. But if your a student who needs something for a project and it's a choice between voiceover and eating, I'm not going to steal your mac-and-cheese, dude. Of course. outrageous demands will not be met and will be refunded.

Who owns the rights? Can I use it commercially?

All rights to the recording are transferred to you. (This is called a "license buyout" in industry jargon.)

You can use the recording commercially, and in any broadcast medium in perpetuity. (That's forever)