This is a silly way to start IMO. You don't say anything about security any measures or anything, and a lot of girls would laugh at only being paid ?100 an hour, if that rate suits you then great but I really think you need to think this through a lot more than you actually have. It's really not a game.
I disagree MsK, depending on where you are ?100 per hour is an acceptable amount for example in the North East the going rate is ?80-?120. And as long as security, cash and boundaries are sorted out it can be fun.
Lucie, my advice would be to look on Adultwork for girls in your area and see how much they charge.
If your friend who made the original joke is open minded, ask her to be your security buddy (if she isn't use the search bar at the top of the site to look for other girls in your area who can help) then when the arrangements for the meet are made, give the time, date, venue and information on the client to your buddy and arrange a time just before and just after the meet so you can tell her you're ok ( you may wish to make up a safe word to use incase the guy isn't as nice when you're alone and you need help)
ALWAYS take the money upfront, I normally take it, go to the bathroom to freshen up and stash half in a make up bag and half in the zip part of my handbag, just incase he decides that after having some fun he wants a refund.
There are loads of other tips on the main saafe site.
Good luck and have fun!