We don't actually know how much it cost as Yu Suzuki himself has said two different numbers. 80 to me, seems far too high even back then personally.
What I'm saying is, they wanted Shenmue to be a big title for them and they poured money into. However, expecting Shenmue to "save" the DC even back then was ridiculous. It was already dying before it was released and it's unlikely one game would turn that around. Throw in the theory that it needed to sell twice as many copies then the DC sold just to hit profit and it's even more absurd.
Take the stupidity of that out and simply work off the the number of DC's around, it sold well. On a more successful console, maybe it would of sold even better? We'll have to see I suppose.