Alright, you can call me ignorant, but....If you see a price for escort with another girl, is that just her price and you still have to pay the other girl or is that for both?

it probably is.

If her rates aren't around double her normal rate, I would guess that it's just her rate and you'd have to pick up the other girl's rate.  They usually have a preference for a doubles partner so it pays to ask who and get the rate for both together.

Bob