> I expect next go-around they'll want to pay some big design agency for a custom site; it'll probably be six figures. I don't know how I should approach that discussion. Any ideas?

Keep your ear to the ground and when you start to hear rumblings of this happening, pay a skilled freelancer to update the old website (or just build a new one if its easier) to fit the new marketing director's taste. Solve marketing's problem, save the company a bunch of money, be the hero.