Personally, I'm a fan of Azure Standard. I am fortunate to live in a western state, on a delivery route (they deliver in 15 states), so I never have to pay for shipping, but there are other options too.
By way of comparison, I ran down a few of the biggest mail-order and online companies with the comparison item of dry organic (or natural) black turtle beans by the 25 pound bag. Shipping assumes ground shipping to UPS zone 4.
Aaoobfoods.com $45.15 Shipping is $13.56* (variable by UPS zone)
Amazon.com (don't underestimate Amazon!). $27.70 shipping, $22.45.
Azure Standard $21.85 Free shipping in 15 states, otherwise UPS rates apply.
Bulkfoods.com $30.81 shipping $5 on orders over $75
BulkWholeFoods.com $30.81 plus $22.63 shipping
Pleasant Hill Grain $67.70, shipping $45.30.
WaltonFeed $45.15 plus $15.28 shipping.
One thing that I can tell you is that across the board, the natural food web sites are very difficult to use. They are disorganized, or lumped (you might find beans under grains or vegetables, etc). They also often have "iffy" ordering systems that aren't user-intuitive. Often, the best solution is to buy a catalog (usually around $5) and then phone in an order.
My greatest surprise here was that Amazon.com carries so many natural foods, and often at affordable rates. If you aren't on a route for Azure or WaltonFeeds, Amazon might just be the best bet, and certainly, for convenience's sake, it's the easiest to use.

