The EE website certainly eliminates every single other variable for making a price and weight comparison. I suspect that the sales price difference closely tracks their cost difference, but it would be easy to check against bulk down prices since the EE selection tool gives you precise weights of down for every combination of temperature rating and fill power. That seems like a good place to get calibrated on market price. If you see comparisons on other seemingly-similar products that are way out of line from that it's probably either a great deal, a ripoff, or a subtle but possibly-important/expensive feature difference.