The DIY part makes it inherently
cheap. Wood and high quality drivers don't get crazy expensive and you'd be hard pressed to spend more than several thousand, the expensive part is having the space for a workshop, and a dedicated listening room, which isn't practical where I am based
And yes, measurements are an important part of the process. Helps you tune the equipment, helps reduce or identify listening biases, helps you understand the room.
High end audio (without the DIY) is where it gets expensive. It's very easy to find 10K amps, 50K speakers. There is a crazy amount of magical thinking in audio, and developing an interest in the DIY side of things helps combat this.
The wood generally doesn't matter, it's more an aesthetic choice. There's a very good case to be made for using high quality plywood for stability reasons (solid woods risk warping over time) then veneering the cabinets. The main thing is you want the material to be stiff but not resonate. Wood is generally good at damping, whereas something like metal is terrible.
Vinyl- that looks like a nightmare of equipment selection and optimisation, then you need wads of space for a collection. I never want to go down that route
This is what I'd want to build when I have the space, though theses don't involve woodwork at all.
http://www.linkwitzlab.com/LXmini/Design.htm