Another observation/recollection from inside the Custom Bass rabbit hole:
There's 2 kinds of 'custom' basses:
FIRST is what I call 'Custom with a Little C'. You know, a custom bass.
This is some combination or minor variation on a body the particular builder already builds. A 'regular model' for the builder in question, and you suggest a non-catalog finish, wood, etc., a different combination of features or options he already offers.
This is like asking the Fender Custom Shop to build some unique version for you of a Jazz or Precision.
It's an instrument they've already built a number of, have the production technique down pat, not a lot of 'off the menu' add-ons. This will help hold the price down.
And since it's familiar territory, both you AND the builder can talk effectively about what you want. Since it's a variation of a known model, the chances of success are high, and if it's not too outside the box, it may well bring a good resale.
SECOND is what I call 'Custom with a Big C'. This is a CUSTOM BASS.
This is where you've thought up something at least completely and utterly different instrument than what that particular builder normally turns out. A true 'one-off'.
This is like asking the Fender Custom Shop to build an Alembic six-string with all the bells and whistles. Or a bass shaped like the Starship Enterprise. Or a potato. Or asking Alembic to build you a doubleneck, bolt-neck authentic Jazz Bass.
Now, there are builders who can do this, but not nearly as many: Most are smart enough to walk away fast. Here, unless you live close enough to routinely stop in and maintain a tight relationship with your builder, this is asking for an expensive disappointment, as you're likely asking a stranger to read your mind and make you exactly what you had in mind which is completely out in left field for most builders.
It can be done, but it will take a long time, probably very expensive, and the chances of the train coming of the track are very high, unless the whole process is very, very collaborative, and personality-wise, you and the builder are sympatico. Don't be surprised if half the stuff you dreamed up is in a practical sense, impossible, unless you have rock star or Tony Montana money to throw at it.
And later down the line, after years of acrimony and insults hurled back and forth, you can get on TB and rag on the guy about 'all that money, and LOOK what I got', and even later complain you sold it for pennies on the dollar and moan about the bath you took on that %&#$&($# bass.
Looked at Squiers lately ? ? ?