So the rear lower black trim/valence with trapezoid oem openings is $175 oem from bmw:
https://parts.bmwofsouthatlanta.com/...127384333.html
AFAIK it doesn't need paint - it comes black stock. So you can just remove your 35i one and install this stock 50i one. All small reflectors - can be just transferred from your 35i to 50i valence.
The only thing is you'll need trapezoid tips and they are kinda expensive:
https://www.ebay.com/itm/New-2014-17...8AAOSwNFFbFOXk