I've been researching this topic for weeks and finally came across this thread. Amazing write up. There are so many but this was very thorough.
Has anyone answered the cost question?

3.0/4.4 – Aluminum Running Boards WITH Front Flares and 4.8 Style Rear Flares.

NOTE 1: Must buy RB Retrofit Kit (51710017315). Also, get the additional parts below which will REPLACE the wheel arches in the RB Retrofit Kit with FLARES.
NOTE 2: If you already have RBs, then you ONLY need the the parts listed below and 26 Blind rivets (51717002953).
NOTE 3: The Front and Rear Flares are DIFFERENT for vehicles with or without RBs.

Part Number ------ Description ------------------------- QTY
51 11 7 073 517 -- MOUNTING PARTS SET (REAR SUPPORTS) -- 1
51 12 7 046 919 -- REAR SUPPORT BUMPER TRIM, LEFT------- 1
51 12 7 046 920 -- REAR SUPPORT BUMPER TRIM, RIGHT------ 1
51 71 7 051 035 -- FLARED WHEEL ARCH, REAR LEFT -------- 1
51 71 7 051 036 -- FLARED WHEEL ARCH, REAR RIGHT ------- 1
51 71 7 051 037 -- FLARED WHEEL ARCH, FRONT LEFT ------- 1
51 71 7 051 038 -- FLARED WHEEL ARCH, FRONT RIGHT ------ 1