yes parking for free at fenway is tough but there's a dead-end side street (referred to on maps as Burlington Ave) just off Brookline Avenue at the corner where the Ace Tickets office is, a couple blocks past Fenway. It's legit, free, on-street parking. As you might expect, it's also hard to get. But it's always worth checking before you pay $40 for lot parking.

for fenway parking you can go near Audubon Circle in Brookline, there are street meters and walk to Fenway (10 min tops) or take the Green Line C to Kenmore Square. If you do, stop at the Beacon St. Tavern for pre-game drinks and snacks.

for parking at fenway try the part of Newbury Street along the Mass Pike that leads to Brookline ave is always worth a shot.   Google Newbury and Mass Ave and look for the part of Newbury Street that runs along the Massachusetts Turnpike. It's all free street parking along there.  It can be kind or tricky to get too though because you can't take a left on it from Mass Ave.  It's best to go down the other part of Newbury and cross over Mass Ave.

parking at fenway is rough so before i say anything else, know this: be prepared to walk. That is the price for cheaper, and its worth it. one option is to go to a nearby hotel and valet. that is sometimes cheaper. next option is to head closer to BU (Bay State Ave area) or Back Bay and look for street parking. Other option is to park in JP or another neighborhood (just check for permit parking signs to avoid tickets) and take the T "