I think it will be tricky to pull off, but i bet it could be done, especially if that's what he really wants (hey, we get to be princesses, why not let the guys be a prince charming if they want!!). I would suggest looking at movies and online, and getting ideas of what you and he both like, and having one made for him. I did find this cinderella costume recently and my mother told me there are prince deluxe ones too...
http://www.costumecraze.com/PNCS55.html?c=cj,PNCS55?c=cj
But I think if you could find the right outfit it would be really fun and also very attractive! I think with the wrong costume... well, not so much!
On a side note, we are having our kids dress up for our VR (wedding fairy, and knight in shining armor), and definitely doing a fairytale theme, but my husband is probably wearing a modern kilt set (the first page of my PJ has pics if you want to see, my dress is on there too). I'm working on finding a costume for my son that will still be somewhat elegant for the event. My daughter will likely just add wings to a flower girl dress, so that will be easier.
I'm currently debating what the knight in shining armor (aka ring bearer) should hold to carry the rings. Glass slipper? Something fairytale like? You might be able to also do a more prince like tux (like the tailcoat I think they are called?) and accessorize more fairytale items to keep your theme, if you don't find a prince outfit you really like.
Goodluck!!