Approximately $1400 in materials and 200 hours in labor (although I could build another one a little faster) - that's what you are going to pay for a high-end pack. 3D printing filament only came to around $60. The light and sound kit was $350, then you pay for all the metal knobs and switches, cables, wires, tubing, lenses, Clippard valves (they are real), resistors (also real), decals, the shock mount, the metal V-hook, paint, hardware, the ALICE frame and straps, etc. I never set out to pay that much, but once you're in the middle of the build, you want it to look right.
If you wanted to have a cheaper pack with things like most of the metal parts, resistors, and valves 3D printed, you could probably make one for $600 or so. It's the light and sound kits that are going to be the biggest chunk.
If someone asked me to build one for them like this, I wouldn't do it for less than $2500, and that's actually a good deal.