Sorry to hear about the back being out, that does make doing things alot more difficult. The Onset Bay Marina has a price chart on line. I was hesitant to post a link to it, But it should be one of the first links with the google search. Bass river probably has theirs online too. Not sure about Nauset, depending on the location they might have tidal access restrictions on the inlet.
As far as transient slips it's pretty easy. Just call the marina your interested in and ask if they have one for the number of days your interested in. It's usually a few bucks a foot per night or so depending on the place.
Trailering is a pain compared to having a slip. It certainly has pluses and minuses.
Good luck, Hope to see you at the Boneclave again, looks like we'll have a better turnout than you and me last year.