Do you keep them or sell them when you're done?
I do the builds and then drive them. Not really into the racing scene around Chicago but I like to find areas and just drive them.
Usually the time invested from start to finish is a huge investment, if it's not working on the car then it's the sacrifices like the 'eating ramen and hotdogs' til next payday cause you just spend $900 on an exhaust.
But also, once the car has been used up and the parts start breaking, they get so expensive to replace or if it's newer than 1995, the dodging the state emissions and trying not to get your driver's license suspended, I usually end up dumping the car to selling it to a friend.
Granted not all the things are 'broken', just worn out and what I would considered replaces. Brakes and discs are one, but for someone that wouldn't drive really fast and get stock OEM parts, it's not bad when you know the car has a newly swapped engine and parts.