Is the missing ADs revenue the crux of the problem?
Instead of raising API price, what if Reddit injects ADs as real content for non premium API calls, so those API free riders/crawlers would get ADs indistinguishable from content. Well intended apps like Apollo could allow users to provide their premium identity and get AD free content. If this works, Reddit could even lower the price of premium account thanks to increase in AD revenue.
Also, I believe Reddit should share ADs revenue with subreddits moderators. This would truly align the incentive of all parties.