1 turbo, with all the assessories can be done for as little as 1k for good quality if you shop around and do most the work yourself. I don't know the specs on this one, but a good rule of thumb is a turbo can add 1/3rd HP back to an engine. If the stock 5.4 3v is pushing 300hp stock, it's basicly 400hp turboed. I think you're stock engine can't push more than 12psi boost, so it's wise to do a rebuild if you plan on pushing that or higher. If you decide to install two turbos, you're really just making boost last longer. Once your first turbo reaches it's max it shuts down by opening it's wastegate valve, and the second turbo engages and pushes you the rest of the way. This is because 1 single turbo cannot hold the RPMs from low to high with out seriously putting strain on it. You could cause the turbine wheel to explode, or even worse IMO spring an oil leak and lose most your oil at it's most needed point. So twin turbos are safer for the engine, more complex to install, and more expensive, but I wouldn't bother going twin unless you were strait up taking it to the track.
