The cances are you will need to pay something for a venue, and will need to buy some resources and a small amount of food.
You don't want to be out of pocket - so you'll need to charge something to cover your costs.
This will be different depending on where you are, how lucky you are with venue, etc.
Here's an example simple budget for sessions: breaking even over 3 months.
Light is an easy to read font, with tall and narrow letters, that works well on almost every site.