1. Fly to Boston and watch the Red Sox in Fenway.
You've never experienced baseball quite like this. Should be less than $250 per person to fly there in June and the ticket to the game can run as cheap as $35 each from Stubhub.
2. Rent a car and drive to Cooperstown, NY for the Hall of Fame.
The whole town is baseball-themed and just begs for two days of your trip. You will need two more to drive there from any major city. Unlimited mileage plan necessary.
3. Get to New York to see Yankee Stadium before it is a parking lot.
I may hate this stadium but the history (even if it has been refurbished) is evident. Amtrak will get you there for about $100 from anywhere on the East Coast.
4. Visit Seattle's SafeCo Field and Pike's Market.
The last time you saw it was the 2001 All-Star Game on TV and you wished you were there for Ripken's home run. Go now and visit one of the most cosmopolitan cities in the US and the most underrated park in the MLB. Alaska flies direct from most cities.
5. Watch your team on the road anywhere new!
Even if you are scared of Cleveland, go watch your team play the Indians and see a new park. Dress in your home-town gear and harass the hapless homers who think Willy Mays Hays still plays for them.