No–one should be making money out of the Jam, but it’s OK. to cover your costs—either via sponsors, or by charging admission.
Some people prefer a free Jam, but others argue that if people pay, they are more likely to show up.
You should decide whether or not to charge admission or costs for your Jam—and if you do charge, how much is appropriate and neccessary. We have seen Jams priced between 5 and 50 US dollars a day, depending on what was included (food, coffee, and else).
Remember, the Jam needs to be open—so don’t be too expensive!