Just thought I'd add this note. My first fretless bass sucked. It was a Yamaha with a P pickup, horrible action, and no personality. My second was the SX, which was worse than my first. Because I was unsure whether fretless was right for me I bought the cheapest basses I could get. I therefore hated fretless and never really got any good at it.
Then I bought a fretless Warwick. I couldn't put it down. I finally got myself to the point where I was able to take the bass, as my only bass, to gigs. That would have never happened with the other basses, and there was no way I was going to put the time in to learn on them. They just weren't any fun to play.
I've since then picked up lots of fretless basses. Picked up some squiers that were set up nicely, and while they weren't warwicks, they really had some nice stuff going on. Made me want to play, and I had a tough time putting them down.
I think a lot of people make the mistake of buying the cheapest fretless they can, and pay the price of never using it or learning how to play. For an extra $100 or so I say don't sell yourself short. Go a step beyond SX. It's totally worth it IMO.
Also, there are some other fretlesses that are fun to play. I picked up a Ibanez SR300, new for $180 last year from American Musical. Ibanez seems to have raised their price on those, but it had a really slim neck, was easy to play, and was incredibly versatile. You might want to give a go at some other stuff also.
