Sounds reasonable to me 20-30% is do-able and would keep the price as is.
However, I would like there to be quite a number of them on the map trying to keep mob spawns in same ratio that soldiers are in for_fild02. Of course this would probably go without saying, but with ease of access comes more farmers, more farmers, less mobs. Could get semi problematic. Hence why I suggested the quest to get inside of said map (see below)
But now as for what mob/where:
My suggestion is to add a recolored soldier;(Soldier of Speed, white or Red?) since the mobs spawned by the turbo room are probably scripted specially.
And as for where, would it be possible to clone an existing map and re-use it for this. And if so could we make it a "cave map"?
Would also like more input on the quest aspect of this, and is it reasonable in your opinions to have a quest to open up the map for the player?
If not then could we add them to an existing map or clone a map and add it to the list of for_fild?
Win Win scenario imo.