Re: 2005 F-150 stx 4.6
It's not as easy as you might think just to slap a turbo or supercharger on. You could get a mild basic system for around $3-4K from Paxton, Procharger, etc. There are several out there. Systems for the 5.4L are easier to find as there's more selection.
I wouldn't push more than 3-4psi of boost through a stock engine (ie, stock pistons/rods/gaskets) or you're fun will be short lived as you'll either blow a gasket, burn a piston or melt valves. All of which, aren't good. Running a mere 3psi of boost won't net you reasonable gains for the initial cost. If it's a fully intercooled system you might be able to get away with up to 6psi, but I wouldn't even trust that without digging into the engine.
The 5.4 can easily handle 4-5psi stock without many upgrades. In light of what you may have heard, the stock fuel injectors can easily handle up to 8psi of boost, so you don't have to get new injectors despite of what others say. Adding too much fuel will just cause it to run out the exhaust (very rich smell) and screw up emission components.
Perhaps others who have done more serious mods on their 4.6 will speak up!
'11 Ram Quad Cab 4x4 SXT 5.7L HEMI (stock); 48,500m
'06 Pontiac G6 GT 3.5L 220hp; 64,000m
'12 Chrysler 200 Limited 3.6L 283hp; 28,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!