I seem to take a lot of local ferries..here is my take:
For WH it depends on the date...if you are thinking off-peak season it is not that bad...but for peak season on a Friday or sunday night it can still be a pain. For the derby (sep/oct) make your res soon....like real soon. If you wait to a couple weeks before you go...forgetaboutit unless it is Nov-April. (cost 55 bucks each way for your car 5.50 for each bassfisherman, 10 bucks per rod (only kidding on the rods)
Nantucket: painful in the summer to get a res with cars, not as bad in the off season, (no derby) but the ferry leaves from Hyansis and it make far fewer trips to Nantucket then MV and most of these get gobbled up by vacationer's making summer rentals in Jan and Feb for July and Aug. After the kids go back to school...you have a more realistic shot. (brace yourself...something like $165 each way + 13 bucks for each bassfisherman)
http://web3.steamshipauthority.com/ssa/
BI: not bad off peak times, summer is a pain but still do-able. I always seem to get lucky with the BI ferry and get on.
http://www.blockislandferry.com/ something like 50 bucks RT for a car.
Orient Point LI to--drive-> Montauk: The ferry is huge and I rarely have a problem..but again, holidays get booked. (standby seems to go pretty fast)
https://www.longislandferry.com/Default.asp
37 each way for vehicle
If you are thinking about going, set a date and call. Also, they are now enforcing the 1/2 hour rule more this season...you better be there 1/2 hour ahead of time or you lost your res to some sap sitting in the standby line. (probably me

)
I hear the High Speed ferry from RI to MV (I think it may leave from Quonsett) is going to be pretty high-end...like a $100 RT -ticket. Thats what I "heard" , I don't put a lot of faith in that number but I think it will be expensive side and will cater to the Nuvo East Greenwich folks who have summer homes here.
I would like to see a S-B Block Island trip...we could cover the entire island and really mow them.