They do offer 10 pass packages too. There is only a volume discount on the monthly pass (e.g. 10 pass = $85 and is good for 10 one way/5 round trip rides). Parking is $4 per day - service fee of about $0.35 for paying by phone. No service fee for paying by the machines on site (credit card). No overnight parking.
You can use the ticket app to buy and activate your ticket on your phone. You may have to go to an MBTA office in advance to apply for/prove eligibility for a Senior rate ID. If you'll be parking at the station, arrive early to find one of the few non-permit spaces, $4/day. If you're a Sharon resident, you can get a resident sticker from town hall. That oks you to park in the non-pass resident spaces on the south bound side.
It generally takes around 30 minutes to get from the Sharon stop into Boston (depending on which Boston stop: Ruggles, Back bay, South Station), but depending on the time, they may have express trains as well. The senior tickets are 50% off the normal fare, which means it should be about $8.25. There is only a single trip, round trip, and monthly pass, no weekly one.
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