Do I need to pay for me alone? I want to set up and do some fletching, eat my lunch and I hope, chat with whomever asks me what I am making.

Is there a Parking/Entrance Fee at Endicott Park? Yes. There is a parking fee on Weekends and Holidays of $1.00 for Danvers resident vehicles and $3.00 Non-resident vehicles. Weekday donations are appreciated https://www.danversma.gov/question/is-there-a-parkingentrance-fee/#/city/answers/park-permits-culture-recreation/is-there-a-parkingentrance-fee

No. I don't believe you pay ever off season and even during the spring through fall it's just a donation as long as you are a Danvers resident