I paid $400 for the install on my LCI 335xi. The shop had to do some extra adjustments for fitment and didn't charge more than the $400 estimate. It all depends on the shops experience and the pipes you bring and how well those pipes will fit without fitment issues. There's other DIYs in here where people who have done the install will testify to how hard it is.
'10 AW E90 335i X-DRIVE M-SPORT
JB+ | AFE DCI | UR DPs | BMW PE | ALPINA B3 TRANS FLASH | 10MM FRONT,12MM REAR ECS SPACERS