Got some friends in southern New Hampshire who run a successful CSA. They charge $525 for a full share, from early June until the end of November. A share consists of 8-10 "items" per week. An item could be a head of cabbage, a bunch of scallions, a head of lettuce, a pound and a half of carrots, you get the idea. They let you choose your own veggies for your box, which is great. If you don't like beets, you need never get a single one. If you want your share for the week to be nothing but carrots (say you want to can a bunch of them) that's OK too.
They have a pick-your-own area where you can harvest your own herbs, flowers, and some vegetables in addition to what's in your share box.
One share is plenty for a family of four, assuming the family eats a fair amount of veggies. Works out to be about $20/week. It's a really good deal. If you're really smart about it and work diligently to can or dry any excess you might have, you can go a long way toward a year of veggies for that $525.