$1.8K for a "4x4" package seems pricy to me. Technically, it's not a 4x4 system it's an all wheel drive system.
To keep a standard gear (not ///M diffs) oil service into perspective below is parts list (OE vs BMW):
- Front diff 1L G2 gear oil ($25-$100)
- Transfer Case <1L DTF1 gear oil ($36-$66)
- Rear diff 1L G3 gear oil ($25-$130)
- Transmission Service Kit, pan w/filter, bolts and 7L of oil ($250-$600)
- 4 Diff fill/drain bolts ($24-$40)
I'd ask for a very detailed list, line by line, of what is included in the 4x4 service. Worth noting the entire service is DIY, but the transmission is the only item that has specific procedures. Front diff, transfer case, and rear diff combined are on par if not easier than an oil change.