exhaust manifold is only for turbos.
The reason they are up to 1000 is that they are for BMWs. Go look for headers on hondas or mazdas and they are around 2-300. Your just paying for the name.
Get a filter and adapter plate off ebay. Then go buy some 3" exhaust tubing from advance auto parts and make your own with rubber elbows or bend the pipe if you have access.
Either way no matter what you do you wont gain much power because BMWs (at least up to e36 im sure) dont come with adaptive ECUs. So no matter how much you put in the ecu wont remap the fuel curve, so your gonna have to get a new ecu, the best of which is a Jim C chip or the shark depending if your obd1 or 2.
Personally i believe the absolute best bang for your buck is getting high compression pistons. That will up your torque a shitload and getting pistons for only around 800 is awesome considering thats how much headers are and headers arnt worth shit. Then considering the money to install the pistons maybe another 800 or so. But you will have very much more power.
<span style='font-family:Geneva'><span style='font-size:14pt;line-height:100%'><span style='color:red'>Fox</span></span> <span style='color:gray'>the Pirate</span>
Diplomacy is saying "nice doggy" until you find a rock.</span>
I live my life one quarter mile at a time, and for those 23 or more seconds I'm free.