If you want to sleep peacefully, the cost of spending the whole night with a SB is a few previous dates plus treating the girl as if she were your girlfriend.
If she agrees to stay overnight the first date it's because: a) either you're very hot, b) or she's a camouflaged professional, c) or she's going to fleece you as soon as you fall asleep.
If a) is not an option, better if you call one of the indies in TAG and she will give you a joyful and safer experience.
BTW. You keep wondering how much? If you have a good long relationship it is the same cost as a date. If you want to please her, give her double or triple the compensation of a regular date.