How do you put a price on your project car?

I was just curious of how others put a price on a car that they built. If they want to sell i

I'm thinking around $25,000.00. Mopars are high in Missouri. There's a guy that has a 1969 dart with a 273 and ps, pb, ac, needs headliner replaced and seats redone. I don't know how good it runs and he's asking 20k.
Got a nice factory 383/4 speed body 99 percent rust free beautiful paint does have tubs but not butchered. How about 25k and at least you would be starting with something that's worth real money when you are done not a 318 car.