But I've been promised these things in the past, and wasted money on them. 99 Designs, Freelancer, ThemeForest (including asking the theme developer for customisations). I've tried them all, and they've never worked. So I approach this fairly sceptically.
But I'd love to see it work.
Usually the biggest problem is not the up-front design - there are some lovely ones out there. It's "how do I map this solution for this problem into a UI that makes sense?". And I can't imagine how you systematise that, but it would be amazing if you could.