It's important to keep things in perspective and in comparisons it must be apples to apples. Most people don't do that. Which is why I said there's too many variables, you can't just make a blanket statement that prices have gone up. A $329 inside cabin on Carnival can't be compared to the $899 balcony on Princess. Both would be considered excellent prices for a seven day Caribbean cruise in their respective cabin categories and the respective cruise line. One in an inside cabin on a Mass-market cruise line, and the other in a balcony cabin on a Premium cruise line. Now, if you were to compare last year's price of the $329 inside cabin on Carnival to that same ship this year, same time, same cabin, and the price was $529 you might say "wow" prices have really gone up. But then there's still all the variables to consider. Are you booking exactly the same amount of days prior to the cruise, is the cruise line offering the exact promotions (past guest, resident,etc). Today for instance Carnival has a 72 hour sale, it can't be compared to someone who books the same ship and cabin after the 72 hour sale.
I'm sure I've gotten too technical, so here's the bottom line. If you want to book a cruise and the price sounds good then book it. Don't worry about what it was a year ago. It is what it is. If in your mind you're happy at the price then that's all that matters. Don't listen to what other passengers on the ship are bragging they got their cruise for, because they aren't adding in all the taxes and fees or they're lying. Personally, I think booking six-nine months out or more is best, but if you can drive to the port and wait for last minute sales then it may or may not work for you. Whatever you pay, the most important thing is you're happy and feel you're getting value. Happy Cruising.