As Shane said above, Acidwashed is chemically etched, I would just add that it is typically then stonewashed as well. That would explain any price difference, as both blades are stonewashed, but the acidwashed goes through the aditional process of being etched first.
Acidwashed will also be darker due to that process, whereas stonewashed will just have the general color of steel. Similarly, some blades are coated and then stonewashed, like the ZT "Blackwashed" finish, which is darker still.
As for the mirror stonewash, I'm not certain, but I assume the process perhaps involves giving it a mirror finish prior to the stonewashing process. I know with Hinderer, the "Working Finish" is bead blasted, then stonewashed, giving it a less reflective finish than the typical Hinderer stonewash.
EDIT: I should add that there are some good tutorials out there on YouTube on how to acid/stonewash, which would gives you a visual explanation of the process.