By the hour and "platonic time"
I don't entertain any "non pros" who want to be paid by the hour, platonic or not.
A very modest "gift" for a platonic first meeting is okay. And I sincerely doubt any girl could earn a decent living getting paid $50 to go to lunch. Also there is kind of an inverse sliding scale where the nicer the restaurant I take them to, the less I am willing to pay as a "gift". Down to the point where if it is a serious high-end restaurant there is no way I am gifting anything. Since I am usually hitting up girls from smaller towns the local restaurants aren't usually very impressive.
The girls who are serious about this and need the money are going to move things to a more intimate level pretty quickly. Usually you can tell in the first fifteen or twenty minutes at the restaurant whether it is going to be on for that night.