Read the header and manifold thread and learn. Headers come with the down pipe, so just buy the headers.
For headers to be effective, I assume the downpipe needs to be in place.
I was aware headers come with a downpipe.
You said you would need the dp for the headers to be effective............ headers are $250 ish on ebay now.
it really depends how far you wanna take your car...
basic DD and want just a little more pep? downpipe...
plan on going beyond a 3.4 pulley? headers...
personally i have the zzps but everyone has their spacific preference....