Take for example, the maple for a double wide, 3 shelf rack probably runs Chris $350-500, which means he’s making maybe $~900 in profit. Subtract freight shipping, and finishes, and you’re at $600-700. For a business owner with the overhead of a small shop, that’s maybe 3 days work.
Now, I could build you an audio rack in 3 days, and I can tell you it would be more utilitarian, than a beautiful piece of furniture. There simply isn’t enough time in 3 days, to take 85 bd/ft of rough maple and turn it into a finished audio rack, unless you forgo quality, and details.
As simple as the design is, it still takes an immense amount of time. The maple needs to be jointed and surfaced on 4 sides, glued up (allow 24h for the glue to set), then trimmed down to the final size. Then account for sanding everything, through 4 grits. Then begin work on the uprights, again, surfacing down the 4 sides, then notching out a nice tight fit for each shelf, then partial assembly, drilling the holes for the bolts, ensuring they all stay centered. After this, you usually begin the finish work, chamfering edges, double-checking for accidental nicks (which are steamed out), and ensuring there are no sanding swirls. Only then can you begin to apply the finish, which is a whole process on it’s own.
Most of these processes can be rushed, but then your work shows it.
If you want to spend $1300 on an audio rack, you’re going to get an audio rack made in 3 days. Personally, I charge for an extra 3-4 days work for a similar rack, and take the time to make it right. Both me and Chris probably make similar hourly, but it’s up to you to decide which you want to pay for.