First, no need to replace all 6 injectors. Was the injector recall done on this car or not? If not you might want to see if you can get a goodwill repair compromise. If it was, then try running some Techron thru the system with some good highway miles to burn up a tank of gas.
Second, $1800 for 6 injectors is what I fantasize making in my next life. You need to get an indy to do it using BMW parts for significantly less money.