Just about ready to jump in...

For a rockabilly setup?

Affordable would be a set of Superior Bassworks deluxe dirty guts, traditional would be gut strings although they’re expensive.

The Shadow Rockabilly Pro seems to be the current popular hot preamp/pickup RAB system at the moment, although there’s many other options.

 

Mark & Bob’s site is full of great info. IMHO the only decent outboard 2 channel options are the Grace Designs FeliX and the Rane AP-13. That said, the reason most preamps are designed to be on the bass is because the further you move the preamp away from the pickup, the more noise you get from the cables. You actually want to have the preamp as close to the piezo as possible. It’s also handy for making changes on the fly live.

Another option is a wireless unit. While not dual channel, it negates the need for a preamp so well that many people even record using them.

You can also run two inputs into any fender style preamp/amp. One in the active and another in the passive input.
I’ve been experimenting with a mic for the “click” doing just that (see pic). I run the bridge piezo (Underwood or Shadow) into my FDeck HPF into the BiX, and those into the “active” channel of my BMAX. Using an attenuator and an in-line volume, I run a Sennheiser E604 drum mic into the “passive” input of the BMAX. It actually works pretty well. It’s a bit overly complicated, but I was experimenting using what I have.

All this would be made easier using something like the FeliX, or the Hedway EDB-2, etc.

 

Also, just do a search on High Pass Filters. The FDeck is the only one I have experience with and it’s transparent with long battery life.

Brighton Audio just released a new one with variable input impedance options which could be stellar.

I would add that unlike bass guitar, upright can cause speaker excursions like you’ve never seen and a HPF is a great way to protect your drivers.

 

I used a Sansamp Paradriver for the first time yesterday. It was amazing. Hpf included. Loved it

 

Where are you located? Best bet is to shop luthier/bass shop first, then see if they can put you into a bass in your price range (maybe even used). Really important with DB to have it set up properly, and as you are just starting out you'll probably need tweaks as you go.

 

That's geat to know.

I have been using the bass driver DI but have had loads of issues as it doesn't have a HPF.

Borrowed a paradriver and it sorted all of my problems.

I'm using a hybrid bass, gut a like swingmasters and Realist pickup into the Paradriver. DI straight out of the sansamp to FOH bt also run it into my ampeg ba115 for stage monitoring.

 

Gollihur sells a Rockabilly bass all set up with what looks like good gear for something like 1700 (Estle Louis Ed). Call them up and ask them about it. Those guys know their stuff, and are very helpful.

 

While I'm not using it exclusively for rockabilly, I've been setting up my Alcoa through the last year or so for the eclectic mixture of pizz/slap/arco roots music that I play. I've come down to the following:

Strings:
Mixed, Innovation SilverSlaps E and A and Superior BassWorks Deluxe "Dirty Gut" D and G
(While I really like the SBW Deluxe "Dirty Gut" strings, I may one day in the next few years go with real gut D and G as much as anything because I want to try then out. I'm not sure whose or when yet. That said, I'm sold on the SilverSlaps E and A which have lasted a year so far and are still going strong, and I expect to continue using them on into the future.)

Pickups:
Vic's Pickups Model C (treble bass-wing and fingerboard piezo model)
(The early model of this set was on my Alcoa when I got it, I've since upgraded to the newest Model C version. These Model C pickups perform very nicely and Vic's service, price and warranty are remarkable.)

Onboard Preamp:
K&K Dual Channel Pro ST
(I've added split dual mono outputs so I can run my own amp/monitor and DI at the same time.)

The biggest reasons I've spoken up here are:

(1) to also encourage having an on-board pre-amp: In addition to reducing noise by being very close to the pickups, it makes quick adjustments easy and ultimately gives you some degree of control of the FOH mix. Personally I like the K&K Dual Channel Pro because the only controls that I have to worry about are the volume controls for the two channels; the EQ and gain for each channel are set to my preferences inside the box. I have my pre-amp mounted to the back side of my bow quiver where it's fast and easy to reach.

(2) to add my emphatic praise of Gollihur Music for all they offer the double bass community. I've purchased my K&K preamp, my Innovation SliverSlaps and a number of accessories from Gollihur since last February and have really appreciated their great service and shared wisdom (NFI).

 

Yup... Aside from great functionality, Vic's warranty and service are amazing. He 100% warranty-covered the pickups that were originally on my Alcoa despite the fact that I was not the original purchaser. As documented on his website, he will repair any of his pickups that stop working under normal operating situations. Remarkable.

 

The affordability factor of Vic’s pickups is another plus. I keep a spare mono element Vic in my gig bag just in case the Underwood or Shadow on my Kay or Roadking craps out at a gig.

And I as well can’t say enough good things about Gollihur Music. They’ve been in the game a long time and know what works, plus they have super fast service.