I buy most of my mods used. So many people sell barely used parts because they want to try something different or upgrade to a new car. I also sell my cars stock and part-out the mods separately. It's still expensive but the cost is minimized with this approach. I have been lucky enough to sell some parts for the same price I paid for them.
'04 E46 M3 - Jet Black - Sold
'08 E90 M3 - Alpine White - Sold
'13 E92 M3 - Silverstone II - Sold
'13 E92 M3 - Alpine White - Ohlins TTX, Fall-Line Suspension Arms/Bushings, AP Racing BBK, OE GTS Aero, Cobra Seats, Akrapovic GT4, GMG 4-point, BBS E88