That's a very good point - if Gordon is worth £45M, then surely a player with similar-ish worth a couple of years later isn't crazy at £50M.
Plus we have to pay a premium because we ain't in Europe because we've been badly run for (a couple, a few?) decades and need that to get a player in, even if we will allow them to play rather than sit in a squad waiting for an opportunity.
If he's who Moyes and the club want, I'd get him in. We're at a crossroads where we could make a leap from lower half to European place challengers if we play it right, so take the chance.