i've got examples too.
I needed custom 15x10 wheels for auto-x. Bought steel wheels $150 each, but they weighed more than I wanted. After a few seasons, i found some aluminum wheels $300. So bought the more expensive aluminum wheels, and took a hit (-$100) on selling the steel wheels. Shoulda just bought the light aluminum wheels ($600 total) in the first place instead of $800 the cheap way.
another case, bought an ebay bolt adapter spacer for like 70$. cracked them after a few events, ended up having to get custom spacers made. Only cost $100 because a buddy is a machinest. So spent 170$ the cheap way, instead of $100 the expensive way.
however, being cheap has taught me how to do alot. I can swap suspensions, do my own alignments, change clutches, all regular maintenance, rebuild and install supercharger.
I've saved many thousands by getting my own hands dirty.
for auto-x: '04 Liquid Grey ZX3
for street: '02 Infrared SVT