the thing about japanese natural stones are that they are a sod to mine, and get into a working state. on top of this, they really are the top end of blade polishing, and as such your paying for a very high quality of material.
this is why good polishers can charge a LOT for what they do. skill levels aside, the only way to get a good polish is with a certain quality of stone, and not many people will outlay such an amount of cash. stone polishing is a real artform, and sadly... you need the right kit to do it well.
there are synthetic stones that can produce good polishes in the right hands, but even those are of a high cost due to the care and attention it takes to reproduce natural materials.
its just one of those things.... if you want a certain outcome, you have to pay a certain price.