My neighbor just did a Factory 5 Roadster after the class. Unless you routinely work on cars at least triple the build time the class puts out. I had an ERA 1964 FIA replica. Did the easy stuff but had a professional do the craftsmanship stuff. The good news is a well built one can hold value. Drove mine as a daily driver for 6 years. It had heat but no air. It was a furlough casualty. Couldn’t rationalize insurance on it as an extra car during that time. Sold it for what it cost me to acquire it. Not often you can say you you owned a car for 6 years for the cost of gas and insurance.
You might look at a Caterham 7. 40 to 100 hour build maximum. You can stay easily under $50 if you don’t get an exotic motor. Even with a completely unassembled cobra kit you will probably be over $50 with a mild engine. You can always go to a more complicated project later.
https://www.caterhamcars.com/us/models/assembly