Honestly I greatly prefer corn fed beef to grass fed regardless of economics. Grass fed is nice once in a while, but I think the best is grass fed, corn finished. It gives the meat a much fattier taste, and I've found also gives you a much nicer maillard crust.
Genuinely interested ... I mean, I know where I can go to get either corn or grass fed, but I wouldn't assume that other variables are controlled for. And then the grass fed, corn finished ... no idea who I would submit that request to ...
They sell these varieties all at Whole Foods. Usually Grass Fes and Corn Fed at the butcher section and Grass Fed Corn Finished pre-packed on the side.