There is a only a fee per run that is paid to the Hash Cash at the beginning of the run. It currently costs 3 EUR for the run only (this goes towards the cost of the drinks for the circle) and an additional 9 EUR if you are staying to eat (which goes for the food) for a total cost of 12 EUR for the run and for the food afterwards.

Note that the run and food fee is waived for your first run (and only for your first run with the NH4) so you might as well stay for the food!!!! Seriously, don't be shy!