When I went to cancel Audible after my promo runs out, I was offered something I hadn't seen before:
Audible Standard at $10/mo for 1 credit/mo. Credits do not roll over, you're not eligible for member sales, and you can't pause membership. Apparently you can download books, though.
I did not opt for this plan; Audible also offered me three months of Premium Plus for half price, and I chose that.