Lots of stuff...
The problem is that most good shops will charge you an arm and a leg.... if its THAT good of a shop... but some places can do a nice setup for you that isnt TOO expensive - sometimes HALF the price of a regular kit..
The nice thing about getting a good kit (like the APR turbo-back kit) would be that its done, ready, warrantied and whatever else... so you can bolt it on yourself...
Its your call... custom stuff is nice - but price savings isnt always what you hope for... get a few quotes before you do anything.. and shop around... cheers!