Thats actually reasonable w/ warranty.
You save effort on finding used & having to clean it. Also used has a risk of bad DISA(and they can fail over time). The Disa replacement actuators could be 300 each at the dealer. Plus DIY install effort is 5-6h( repeat if you need to replace a bad Small Disa).
Given the relationship you have at your dealer, do you think your DME can be flashed with z4 3.0 SI or X5 software @ a low charge? or will you go the AA or Eurocharged route
128i Sport 6MT converted to Euro 130i spec, tuned by evolve ~220 whp 207 wtq(ft-lb) SAE
In-progress: e46 m3 trans mnt, e36M lip Wishlist: m3 susp, n55 eng mnt, headers, LSD, finn dif e60
"The 1-series is the last car that BMW engineered before the Germans, as a car-making culture, fell out of love with driving." - R&T 2013 135is