My opinion...
There is only one type of Chrome used in plating. The other types of chrome are: chrome 2 and chrome 6, or hexalent chrome which is extremely toxic. The process usually begins with an electrolytic caustic soda bath that uses electricity to etch or clean the piece to be plated. Then the piece is rinsed to clean the caustic off. The piece is usually flash copper plated to prepare the surface to be flash nickel plated to insure a smooth blemish free surface. Some platers will polish the flash nickel plated surface area to insure a totally smooth surface and then chtome plate the part using either soluble chrome anodes or chrome solution as the chrome source and insoluble anodes and the chrome dolution and electricity to csuse the metallic chrome atoms to adhere to the piece, which is the cathode of the circuit . The actual chrome thickness is very thin...in the neighborhood of maybe 0.002". The time the piece is in the tank, the amount of current used will determine the total thickness of the plate. The piece is rinsed and polished to a shiny luster. These processes take time, labor and energy which will determine the final cost along with the various solutions that are used and their disposal costs, as they are quite toxic. Each platers' methods will vary which account for the cost differences. Just my opinion of course.
BOB RENTON