PPM: Hey, well you're exactly right that there is a lot of variation. I've had asks of 200, 500 and 700. I have no doubt there are some who want 1000 or more.
My general understanding is that most girls are looking for 400-600 kind of thing.
Monthly: you're typical getting more interaction (texts, etc.) and you can figure out the details of how much you're meeting: you're looking at least a few
grand, if not more.
Unlike SP's, though, there is room for negotiation. Meet up with them and, if she likes you, perhaps the rate could be lower than what she typically has in mind.