A single seiza bench begins with a 34" board.
The cuts are as follows:
One piece of 10' x 1" x 6" pine board. $ 10.00 (yields 3 seiza benches = c. $ 3.33 a piece)
Half meter of material. $6.50 in the sample of paisley pattern I chose.
Quarter meter of 1" thick foam. $ 6.00
Total cost: $ 15.83 + screws/hardware.
Under $ 20.00
This is a picture of the seiza bench I made and use.
The nice thing about the seiza bench is that the angle (c. 17 degrees) puts your hips - and thus your spine - at a near perfect angle and allows you to breathe properly.
The sitting position is basically as you would sit on your calves. Your feet and calves are beneath the bench, while your bottom sits on the bench proper.
It is actually a very comfortable position.