great update. Like you said, just make one, simple part so you can get enough funds. Start a group buy thread so once you get 10-20 people you know you will be having enough funds for the project.
It could be something as simple as carbon fiber badges for the rear(128,135i), to a carbon fiber license plate.
Or, if you are 100% certain you are ready, you could design something big and make it cheap, like a front lip.
Personally, I think your best bet is probably carbon fiber mirrors for 2010 + models. Apparently nobody makes them.
I have a 2009, but just for reference, chinese CF mirrors for these from ebay are 99 dollars, autotechnik(german) are 150, and BMW performance are like 500 xD.
2009 128i Coupe Crimson Red
MODS: -Injen Intake-Magnaflow Exhaust-Carbon Fiber Spoiler - Carbon Fiber Grilles - OZ Ultraleggeras - CF Mirrors