<p>We have a dozen calculus books including the Caltech book. But the newer books provide a lot more in the way of applications. Apostol also comes in two volumes which are $140 each (I got Volume 1 free from a coworker and bought Volume 2 used for $20 before prices for textbooks went crazy).</p>
<p>If you’re looking at AP Biology, the material can change rather quickly as it’s a rapidly expanding area.</p>