Depends on what brand and if they are long tube or short tube. I have Stainless works long tube headers w/hiflow cats and they run around $1200.00. That does not include install. Short tube headers are cheaper.
I did my own in my garage, I bought JBA shorty headers, took about 2 hrs but that included 30 mins of beer intake, some cursing and swearing, it isn't that hard, just a small space to work with on eth passenger side, heck even my wife who was 9mos pregnant was helping me... hahaha
put it this way, if you have some mechanical aptitute and some basic tools, you can navigate this install and save at least $400-500 your dealer may charge you.