Logan International Airport
Logan Airport is conveniently located just outside of Downtown Boston; so getting from there to anywhere in the city is fairly easy. Sadly the train doesn't run across the river to Logan Airport so you have two options: you can take Silver Line bus to South Station, where you can transfer for free to the Red Line train and get anywhere in the city essentially. The other option is to just take a cab or Uber from the airport to your hotel. Unless you are going far outside the city it shouldn't be more than $20-$25 and a 20 minute ride depending on that pleasant Boston traffic.
Free if you take the Silver Line to the train. If you opt for an Uber or Cab it will be $10-20 depending on where in Boston you are staying
Generally the cheapest time to book flights for Boston Calling will be about six weeks before Boston Calling. This means you should be focused on booking your flight in April 13, 2018. This may seem late to you planners out there, but statistically it's the cheapest time to book flights. That said, if this is too late for you book it earlier. One final note is that plane tickets for Boston Calling tend to skyrocket about two weeks out, so certainly don't wait that long to book a Boston Calling flight.