I live 20 miles north of Boston, the area is collectively called the North Shore. I have easy access to at least 2 beaches, Dane Beach in Beverly and the ass kicking Crane Beach in Ipswich. Dane beach is a public beach, free parking and all, but the price you pay is huge crowd and coarse sand. The supreme Crane Beach on the other hand is a very well maintain beach , with sparkling white fine sand and nicer facility. But it cost $15 to park, $22 in the weekend.
So as soon as I moved here about 6 years ago (wow), I drove around and found myself a nice free beach. It is nicely tucks behind some beautiful but not flashy beach houses, and a destinated but very limited parking for non-residence. So I'm not going to tell you where it is. Good Harbor and Long Beach in Glouceter are another great beaches, it also cost about $20 for parking. As outrages as it sounds, the parking is always full in a warm summer day.