John,
If there are only 100-200 people in attendance, I am not sure it would be something that would fall foul of any 'big group of people rules'.
Even if it did need permission, if I recall correctly, to land near an open air assembly of more than 1000 people just requires compliance with the relevant bits of AIP Gen 1.6.
Happy to be wrong, it would be a shame to not get this done if it was deemed to be difficult, just in case someone can help.
GS