$40/year for 25 credits
With this choice, join for a year, receive credits for joining plus receive more credits when donating books back! An added benefit is 15% off of any priced book, like those new or listed on Amazon.
This membership basically adds a donation to your membership; they still bring 25 book credits but $15.00 of the Sustaining Membership fee counts as a donation. Of course donations in any amount are always welcome.