I disagree. I think a pair of globally sourced cabinets is going to cost less than the cost of materials and tools I need to buy to assemble and finish a pair of cabinets.
Sure, but that probably means this isn't quite the hobby for you?, DIY is all about enjoying the process of having parts and tools, and ending with a finished speaker.
In reality, It's only "cheaper" when products can be produced in mass volumes. (think 5-10 thousand units per run etc) In many cases that also means massive up-front costs for testing/development of a small first runs, then the final run, all the while, shipping costs, promotion/advertising costs, labor costs, etc. etc. all add up quickly, and most business will likely fail under this pressure unless there is large, and continuous demand.
DIY is meant to cut all of those costs and risks put of the loop, allowing you the opportunity to build a $6000 speaker for $1000-2000. Or a $1000 speaker for $400-500. Plus you get to learn new skills and tools that you can use for other projects down the line!
DIY is an adventure & its all about exploring the possibilities of what might come next!
Why pay an artist $2000 for a painting, when you can just go to the store and buy a poster for $2? Sure, the mass produced poster was cheap, but it probably also was made on cheap paper, using cheap labor, & there's 100,000 copies just like it.
But when you pay an artist directly, it costs a lot more, but you get something unique & special.
While DIY kits fall somewhere in the middle, the parts and design are already layed out, but you get to decide how the final product looks, be it a simple coat of Duratex, stained veneer, or even custom automotive style paint.
Its a hobby that's all about having fun, learning new skills, and getting to enjoy the fruits of your labor.