After you pick your initial winner, you can always Private Message the other designer (hopefully you ranked them second place, if you like it that much) and ask them if they will sell the design to you as well. Most of the time the designer will want the same price as the contest was originally for (because they probably put just as much time and effort into making it as the winner that you picked). But you can ask, and find out if they want to sell it to you.
The only thing that I recommend is not to approach them until the contest is over with, because it's consider a back woods deal. But after the contest it's okay to ask. Many CH's have done this in the past.
Hope that this helps!!
You might want to wait a bit also, you currently only have 13 entries and 4 days left to go. There might be a later entry that might blow your socks off!!