I'd like to chime in as someone who is currently in the process of building a car myself for the December 4-5 Sonoma Race. Here is my experience so far on expenses and time:
Expenses:
Car: $500 (Ford Focus)
Maintenance: $500 - oil change, spark plugs, valve cover gasket, etc. excluding brakes
Safety items: ~$4,000 - including roll cage, new brake rotors and pads all around, kill switch, harness, etc. Everything to pass tech inspection.
That's $5,000 to simply get the car running and to pass tech. Want a cool quick release steering wheel? Add more money. Need a mechanic to do some work? Add more money. Want a second set of wheels and tires? More money.
And this is all for a 2005 Ford Focus, which are super plentiful in junkyards, easy (and cheap!) to find parts at your local O'Reilly's/AutoZone, and with me doing every single bit of work except for welding the roll cage.
I'd also like to point out that I didn't buy the cheapest items, but I also didn't buy the most expensive items. I spent more money on safety items, and stuck with middle of the road stuff everywhere else as an attempt to get some quality for a reasonable price. I spent days waiting for stuff to go on sale or finding the one place to get a set of front rotors for 30% off. Which brings me to time.
Time:
I bought this car in early June, six months out from the race. I'm just getting the last of it done now, maybe 10 days to 2 weeks behind my original schedule. I work on this car every weekend, and maybe 2-3 nights for a couple of hours during the week, and have been since early August. This isn't my first car wrenching experience, but it's always surprising how quickly time gets eaten up by dumb stuff, like having to go to the hardware store yet again for some bit or bob. The roll cage needed to be scheduled 2 months out. Parts take time to arrive. Going to the junkyard for what you want is, at the very least, one whole weekend morning, and you will need to go multiple times.
I'd also like to point out here that I planned most of this before I started, including what should be done and in which order, to maximize efficiency (don't judge me, this is what I do). I was very organized with my time in the sense that I knew what else I could be doing while I was waiting for a specific part or some safety equipment. For example, I had to replace a motor mount, and since I was disassembling most of the coolant system, I drained and replaced the coolant at the same time. I did this as efficiently as I think is possible.
Finally, I'll say that I personally think building the car was/is as much fun as racing the car, so I didn't want to go buy a pre-loved Lemons car. I have enjoyed this experience, and there is no bit of this car that I don't know, or haven't touched. From my calculations, I think Lemons is still less expensive than competing in almost any other racing series, in the sense of minutes driven per dollar, but it takes time and some money to do this right - which ultimately translates into passing tech and getting on the track.
#22 Team Slowtus Ford Focus