The idea is to alter the Reprap Prusa i2 at an absolute minimum cost, in order to get 21-24 cm of print height. Note, that, unlike in Reprap Pyramid, we are not going to purchase longer smooth rods: we'll reuse the 30 cm ones. We are only going to need some (not all) new plastic parts and new threaded rods ($3-4 on a local construction market). The rest: hardware, electronic components etc. - is the same.
Reprap Next provides detailed assembly instructions on its home page (select 3d Printer - Reprap Next to skip intros): Reprap Next