The Bullpen Sports Bar is a wonderful place to go with an awesome environment. You don't have to pay to get into the bar. All you have to show is your ID proving that you are over 21, and you buy your alcoholic beverages like you would at any other bar. I'd highly recommend their lemonade vodka drink. You can find that to your right (opposite the bathrooms) as you enter. If you want to go on the Bullpen Sports Bar porch, however, you must pay an extra $10.
I've been there a couple times, and it is a must for all Sox fans who are of age!!!