VDI texture is done via the EDM when burning the tool. Mold Tech textures are done after the tool is cut and require a combination of etching, usually with an acid bath or other process.
Mold tech requires more preparation (the tool must be polished, prepared (sometimes by hand, depending on the texture type) and then etched). VDI can be done during the initial tool burn so is cheaper, but it is harder to repair and match if tooling modifications occur.
As far as pricing - it really depends on how big the tool is and what type of texturing they are doing. Also there are a large number of houses that do “Mold Tech” knockoff textures but are not Mold Tech themselves.