Claudio; the necks are not all the same. The two standard tapers are Classic (narrow) and Comfort (wide). Plus, when looking at used basses you need to check if the neck may have custom dimensions; it is not uncommon. Here are the dimensions:
4 string
Classic: nut - 1.750, 24th fret - 2.250
Comfort: nut - 1.625, 24th fret - 2.630
5 string
Classic: nut - 2.000, 24th fret - 2.500
Comfort: nut - 1.875, 24th fret - 2.930
Check your Distillate, I can't recall but I think the Distillate has the Classic taper. Essence, Rogue and Europa basses come standard with Comfort tapers. Signatures and Spoilers have Classic tapers.
If you're looking at used basses, you may want to be really patient and, as Mike suggested, see if you can stumble across a Distillate 5 string. Also, you could be watching for a Spoiler 5 string. The only problem there is that most Spoilers are 32 medium scale instead of 34 long scale. Another bass to watch for might be an Elan, although Elans come in a variety of configurations. But Mike is right, if you want to get really close to your current sound, the neck woods and Europa/Rogue or Distillate electronics are the things to look for.
As far as sites to check, the best place to start is here! And then of course Ebay. There are several others, but if you are on a tight budget and can be patient, here and Ebay are the places to start. Besides reading our forum every day, check Ebay everyday and start getting a good feel for prices.
(Edited typo; thanks Bob!)
(Message edited by davehouck on April 28, 2005)