Well as it turns out my used G&L L2500 fretless (happens to be lined but that is irrelevant) is not just 'good' but THE most amazing 5 string fretless I own. It is my main axe and I LOVE it. nothing more versatile and killer tone in all modes. And it so happens I paid $600 for it. But of course that had some luck there. Just saying keep your eyes open.
On the other hand I have a couple SR series Ibanez and I would not discount that choice either. different beast from G&L but still totally killer in it's own way. Look at all those too!
For fretless I tend to prefer unlined (for looks) and an ebony fingerboard (for tone) although I have an SX Fender clone Jazz in alder with a rosewood board that I got for $99 years ago and it's still none too shabby and I still have it, but the G&L is better, but then it cost much more. I see no reason why you can't find a killer fretless 5 in the $600 range.