Charlie Card is free. If you approach any MBTA employee in South Station or Back Bay Station they’ll just give you one and you can load it with your credit card at the machine. I have seen dedicated employees handing them out during rush hour.
You can’t get one in Logan Airport, but you can get take the Silver Line to South Station (which is free, I believe) and get one there. Another option would be take the Logan Express to Copley square ($5) and walk over to Back Bay station, which probably qualifies as the world’s ugliest train station.
Credit:stackoverflow.com‘