North end of LI Sound is a great place to explore. I bought my boat there and moored in Bristol RI for the first year. My daughter lives on Martha's Vineyard
and they keep their boat on a mooring in Lake Tashmoo.
If you have good ground tackle and don't want to spend the big bucks on dock
or mooring I would anchor
in Tashmoo or the lagoon
off Vineyard Haven harbor. Both are very protected and good holding. Not sure the rules for long term anchoring
but there are harbormasters who are very helpful.
Some of the spots in the upper end of Narragansett Bay may be more reasonable as well. In general the further south and closer to the sound you get the more expensive it is.
There are a couple of websites that you can use to research marinas
and rates. I think https://activecaptain.com
has a pretty complete database.