Alternative to Tarbais beans in Cassoulet

I have been on a duck confit jag for the past few months; can't get enough of it. I have been thinking about making cassoulet, which, from my reading, is classically made with Tarbais beans. at $15/pound + shipping, they seem a bit on the expensive side. What are acceptable alternatives and is there a significant difference between Tarbais beans and any recommended alternatives? (Hope I don't set off a holy war between believers and the rest of the world...!) Thanks Ken K

Chicken is pretty close to duck. Is it ok to sub that? Hot dogs for sausage? (Sorry- I'm being snarky but I think beans are THE essential part of the cassoulet.) I'm not saying you must use Tarbais. I'm saying if you're going to all the trouble, why use a crap bean like a Great Northern, which are nothing like a Tarbais? Use a runner cannellini (very close) or a flageolet, which are creamier than a Great Northern yet have a thicker skin so they won't break down in a cassoulet the way a GN might