Yes you can add the auxillary valve. As far as the cost, it will depend on how much of the parts you make your self or buy from a Case dealer. You will need the valve and a way to activate it, power beyond that you will have to get from Case and a tee fitting for the return to the loader valve. You will also need some hoses to hook everything up. The lines going down the loader frame are steel tubes, could be hoses if you dont want to buy them from Case. could be as cheap as $400.00. Around $800.00 to get all the major parts from a dealer.