My fiancee is a lawyer and bills out her time at a little more than $400/hour. If she spends more than a couple of hours trying to save $1000 or whatever off the retail price, she's losing money. So when I say that she's not going to sweat saving a few % off of the retail price, I mean it in pure economic terms. Now, if she was going to buy me a $50,000 watch or a car, chances are she'd shop around a bit for the best price.
With respect, your math is off. While, of course, your fiancee should only shop around as much as she pleases, if at all, it would be quite worthwhile to shop around for more than "a couple of hours". Remember, she bills $400/hour - I assume she has overhead, like the rest of us, and partners, etc. Then there's tax. I figure that after tax, I'm lucky if I make 20% of my hourly rate.