So scratch that.
After booking the tickets through kayak.com, I woke up in the middle of the night last night to a notification on my phone. Apparently, Kayak booked the tickets through yet another discount-airfare site, airfare.com. Airfare.com called me and left a voicemail (at midnight!), saying the cost of my ticket had gone up "tremendously" at the "last minute," and recommending that I call or go online and cancel the tickets, unless I wanted to "pay... [ominous pause] more." They didn't even leave a phone number.
This sounds very un-legit. I poked around online and found a string of freaked-out, one-star reviews of airfare.com, rife with words like "scam," "avoid at all costs," and "kayak.com should have dropped these people long ago."
This morning, I called airfare.com's customer service. It turned out that the "tremendous" price raise was about $100.00, which on a flight to Australia is actually pretty insignificant. But I was skeeved, and I had a recording of them saying they would cancel my reservation with no penalty, so I thought it best if I just got out. I cancelled the flight, and the guy on the phone said he would honor the no-fee promise. I'll have to wait and see what the credit-card statement looks like when it comes back in the next few days. I hope to God this isn't some drawn-out battle with incompetent/malicious customer service.
Anyway. All in all, it shouldn't be a huge loss. It's on my credit card, so I can dispute the charges through my own bank as well, and the price of airfare is still the same, if not a little lower, than it was yesterday when I booked. I kind of want to wait for the refund to show up before purchasing other tickets, but either way, I'll look very closely at who's doing the booking next time.