Me [23 F] with my boyfriend's [23 M] parents [mid-60s, M&F]; I agreed to pay for a portion of my travel for our upcoming vacation, but they booked something way out of my price range. Should I say something?

tl;dr: Boyfriend's family is paying for a vacation, if I pay for my own flight. They booked the flight without consulting me, and it is $400 more than comparable flights online. This seems to be part of a pattern of behavior.
Background/ Situation: I am a 23-year old graduate student. I have been dating my boyfriend (also 23-year old) for about 2 years. Recently, his parents invited me on a cruise to Alaska, on the condition that I would pay for my flight. We live near Los Angeles, and the cruise leaves from Vancouver.
I agreed to pay for my flight, thinking that the flight wouldn't be that expensive. I was correct--they cost about $200-$300 on our travel dates. His dad (~60 years old) booked the flight for us, thinking he was doing us a favor, and got a flight that is almost $700, so we can sit together and leave slightly later.
About my finances: Even though I a currently a graduate student (to be frank, we make