They're quite uncommon, hence I cant find an afordable version. Dominatly they are electric violins. The idea behind adding frets is to allow quick chord progressions for a trditional player, or you could tune the high strings down to standard guitar tuning and that would make an easy transition for a violin dumy like me.
I cant imagine trying to learn without frets. That would take forever, frets are kind of a 'shortcut'. Although you do loose a few major aspects of the violin, it does not bother me because I dont already play. And like I said you pick up soem good features of a guitar.
If I could afford it, here is what I would get
http://www.woodviolins.com/html/sabre.html
Im yet to find a violin with magnetic pickups too - maybe its better that way.
JP