If you're hunting for the 'The Last Olympian' audiobook, your main move is probably checking Audible first. It's got the whole Rick Riordan Presents catalog, and they usually have the full production with the narrator who's done the whole series—Jesse Bernstein, I think? That continuity matters, honestly; switching narrators mid-series is jarring. I grabbed my copy there because I had credits stacking up. Some folks don't love the subscription model, but if you're going through the whole Percy Jackson run, using a credit for each book isn't a bad deal compared to buying them outright.
Libraries are a seriously underrated option, though. The Libby or Hoopla apps link to your local library card, and I've snagged the audiobooks from there more than once. Waitlists can be long, especially right after the Disney+ show drops new episodes and everyone gets a nostalgia rush. It's worth putting a hold on it and listening to something else in the meantime. The quality is identical to the retail version, and hey, it's free. I sometimes bounce between my purchased copy on Audible and the library borrow depending on my impatience level.
Don't sleep on digital retailers like Apple Books or Google Play either. They sell the standalone audiobook if you want permanent ownership without a subscription. I've compared samples, and the audio quality is fine, though the apps aren't as feature-rich as Audible's for bookmarking or speed control. For 'The Last Olympian' specifically, the climax is so dense with action that I like having precise control to rewind certain battle sequences. Wherever you get it, just make sure it's the unabridged version. You don't want to miss a single line of that final fight against Kronos.