I'm guessing the bots are hitting the search page because it contains the most amount of information per hit, and that the caching problems are exactly due to these dynamically generated prices or other such nonsense. After all, the fundamental goal of scraping is to straightforwardly enumerate the entire dataset.

The scale of the botnet sounds like an awfully determined and entrenched adversary, likely arising because this company has been frustrating the market for quite some time. A good faith API wouldn't make the bots change behavior tomorrow, but they certainly would if there were breaking page format changes containing a comment linking to the API.