you dont have a hobby shop on base? i thought most places do?
the 5.4's are not a great motor to start with, they are dogs.
and they are a pain in the ass to work on because they are tight.
the manifold may be cracked, or a broken bolt, or possibly just a bad gasket, in any case, none of them are really that hard to fix, gaskets are like 20$ maybe less, depending on what u buy
a cracked manifold is more expensive but still less than 100$ a side
and if its a bolt then its more difficult fix, (getting the old part out) but dirt cheap