The price is a factor, but it's a relative factor. I agree that most people buying & using M77's aren't willing to pay a significant mark-up for the Express configuration. Then again, most of them wouldn't be willing to pay MSRP for the standard 9.3x62 Hawkeye.
But...I think there are plenty of people who are getting turned on to the 9.3x62 cartridge, and like the traditional styling of the Express, who would be willing to buy one. These are the same guys who know that an integral quarter rib adds between $1,000 and $2,000 to a custom barrel order.
It would never stand as a production offering, but I think the "limited edition" factor and the configuration would get 500 of them sold...not sure if that would make it worth Ruger's time and investment. I also think it would outsell the old offerings in .458 Lott, .416 Rigby, and possibly the .375 H&H.
I suspect the gunblast edition is going to sell quickly too.