Someone once told me that commercial grown Runners are ground growing so they don't produce that many pods, and they have to be picked by hand, that ramps the price up. As most of us know, if you stake them up you get tons of beans which are always less gnarled and pithy than the shop bought...
I think you can eat them whole, pods and all untill they get about as fat as a finger then they start getting tough. Mind you, they are crap beans, almost all other varieties of bean are more edible than Broads.