Properly stored beans should last from 1 - 4 years in storage.
However, bean seed germination is soil temperature and moisture sensitive,
and thrives on heat and even soil moisture.
They should last more than a year, generally more than 4 years under proper circumstances.
Last week, on 'Splendid Table'(NPR/PBS) they interviewed Steve Sando , who specializes in international heirloom beans chilis, and 3 types of Quinoa (Peru) :
What Ray Bayless is to Mexican chilies and food culture, Steve Sando is to heirloom beans.
Steve Sando (Calif) specializes in heirloom beans ,corn, and chilis
He seems to specialize in Mexican , and imported heirloom beans,only.
He does have other products like Mexican chocolate, cinnamon, and Quinoa, etc...
Highly Recommended varieties : "eye of the goat" (currently sold out), and "royal corona" bean " (imported from Poland)
(home): http://www.ranchogordo.com/
(products) : http://www.ranchogordo.com/collections/all (with photos)
He recommends you plant 80 % , and retain 20% for next years, and years thereafter, seed just in case of crop failure.
Prices seem to be reasonable since quantities are measured in pounds (not in # of beans), although shipping charges have not yet been compared.