I think a lot of people stumble onto pirated PDFs because they get impatient, but 'Bluestar' actually has a pretty straightforward digital footprint if you know where to look. I found it on Google Play Books first—it's often discounted there, and the app's reading features are decent. I also saw it listed on Rakuten Kobo, and they have frequent sales that bundle books from the same publisher.
For a more library-style approach, I'd check if your local library uses OverDrive or Libby. I borrowed it for three weeks that way, completely free. Amazon's Kindle store carries it too, obviously, but I try to avoid giving them all my business if I can help it. The author's personal website sometimes has direct links to multiple retailers, which is nice for comparing prices without extra clicks.
Just a heads-up, there's an older edition floating around with a different cover; make sure you're getting the latest version if that matters to you. The page counts differ slightly.