Doing custom work is some of the best and most inspiring time spent for me, tweaking and communicating about something for someone's invididual needs and taste.
I would be happy to take a look at your project, and you can see a few examples of my work below.
The simplest projects usually start around €2000, price ranges upward from there, depending on how complex it is.
Custom buffer unit with an MS matrix, and gain selectable for an IC or Discrete Op-amp path on the output.
Switching insert matrix, fully balanced "invisible" signal path for 8, swappable inserts, and switching on relays.
Custom high- and lowpass filter unit, with selectable filter orders, and frequency selection on relays, matched carefully to 1% tolerance.
Custom STEM mix matrix, with separate sidechain mix, and side chain mix audition, going into a VCA style master compressor.
Custom insert point/buffer unit, gain, gain return compensation, MS, Blend and bypass.