Ideas have been booted about, but to my knowledge nothing has been tried.

The reasons that people come up with for why it won't work are:

• Ducted fans are less efficient than props, so you'll need more battery
• Ducted fans are more "constant force" devices than "constant speed" compared to propellers -- so it's feared that speed regulation will suffer

But, again, no one's tried it.  I would strongly suggest that if you do try it you spend some of your budget on an Igor Burger regulating timer, because that should help the speed regulation issue tremendously (although probably not fully).  I also suggest that you start with something simple (i.e., a lashed-together profile) and go from there.

It has been stated by more than one person in the discussions however, that a semi-scale A-10 Warthog would be the coolest.