Google Books API rate limiting information?

I can't find any information on rate limiting with the Google Books API. I'm interested in doing ~300K total ISBN queries to retrieve lists of book categories, and I want to throttle my requests to stay under their limit. I have a developer API key, but not OAuth. Does anyone know what the rate limits are for the Google Books API, or at least have a ballpark?

According to this post,

https://groups.google.com/forum/#!topic/google-api-java-client/_TFuPpAKSew

Around 100k/day is not a problem.

You can also request more quota, if you need it, as follows:

1. Go to the API Console (https://code.google.com/apis/console)
2. Select "Quotas" on the left navigation pane.
3. Click on the "Request more..." link and submit the form.

"Your quota request should be processed within a few business days at most. Basically we want to hear from our developers so we know what type of traffic they are sending, so we can add resources to accommodate them as necessary. But from what you describe, perhaps 100K/day, should not be a problem."