For 500 yen per adult (elementary school students are free!) you get a bucket and 40 minutes to wander among hundreds of blueberry bushes.
The staff are always very friendly, and there's a covered seating area with free barley tea where you can take a rest. Parking is free, and when you see the giant Buddhist monk statue, you'll know you're in the right place.
Kanga's Blueberry Farm website (no English): http://www.niigata-blueberry.com/