caterpillars

I'm only interested in a particular cruise (Alaskan cruise for summer of 2019 on Princess departing from SF only) but I'm flexible on dates (any date during the summer works).  Would I get a better deal working with Princess directly or using a regular TA?  Thanks. 

I'm looking at the princess alaskan cruises that do round trips from San Francisco.  I live very close to SF and can do something last minute since I live so close by.  My dates are flexible and I'm looking to do the cruise in the summer of 2019 (preferably June/July/August, but open to late May and early September as well). 

What is the best way to go about this?  I heard you need to book a cruise at least 72 hours ahead of time due to passport issues, something I'm OK with doing (obviously the more ahead of time, the better, but I'm looking for a deal here and have the luxury of flexibility and last minute booking).  Since Princess has multiple dates for the Alaskan cruises, I imagine there must be at least one cruise during summer 2019 I can get a good last minute deal on.  I am a solo traveler and I would like to avoid paying double for a room.  This will be my first cruise ever.  

Thank you.