I've just joined here from the Yahoo group.
Adding frets means you've become a viol player. I think you might be interested in this site http://bowedguitar.com/.

You might like to hold off on cutting slots in a finger board and try the viol tradition of gut ties around the fingerboard neck.

I think you ought to realise that the sound changes dramatically as well. Listen to fretless electric bass playing and fretted bass playing. Not the same animal.

though the idea makes me cringe a little bit (I always say "no frets , no worries") my good friend who is a viol player has tied frets to his double bass which he claims makes it easier for him to play in tune. For me, he has now rendered the bass unplayable. They call them gut frets but they are really like heavy nylon fishing line. Definately the cheapest route for you .....I ocassionaly entertain the idea of how nice it would be to have frets to play full chords with a pick in the middle of a show , but then I wake up and realize that I could just get an electric mandocello......

The problem with frets is you lose the ability to slide notes (gliss.)!!!and you lose some vibrato as well. I'll shut up now so I don't have to suffer the wrath of incensed viol players.....!

peace