VorTech MP40w Question

If I was to purchase this item, but wanted a second power head does one need to buy 2 units or can you buy just the power head to add to the first one cause i read you can run multiple power heads. hope I'm making sense here. I guess what I'm trying to say is if I bought the 499.00 dollar one and want a second power head do i need to spend 1000.00 or can you just get the power head only at a cheaper price?
thanks for any feedback.