If you are a welder, you might be able to build your own custom headers for less than kooks. But do it for the learning experience, not the cost savings.
I don't have a 13 sec SC, so take IMHO for what its worth;
but as i opined, headers dont make too much difference on a supercharged engine, which is scavenged by positive intake pressure. [boost]
Manifold-back Exhaust & Gears are best bang for buck mods. [I would prolly be in 13s, but have chosen not to buy the extra fuel associated with 3.73 gears...]
Your engine money is better spent on intake, good heads and cam, intercooler and blower mods.
[edit: not to forget SCT tuning and fuel system upgrades and BHJ balancer, so your Performance mods don't break it]
At that point, the headers might be worth the coins.