Here's a quick DIY for a great looking quad exhaust with a good sound for < $800 total.
Parts list:
$250 Used oem echaust (look on the classifieds on the forum)
$150 Alibaba Quad exhaust diffuser for F30 435i -
Link
$50 Dual tip U Power exhaust tips from Amazon -
Link
Have a local shop do the exhaust mod via this thread:
https://f30.bimmerpost.com/forums/sh...d.php?t=819125
The exhaust tips are a direct weld on and fit perfectly.
Results: