First of all, it's not worth much more than that. Second, it's a nice car in good colors. Third, you did absolutely nothing unethical, which most car shoppers Ould without blinking.
I habitually buy project cars or cars that have been sitting and if it's from a friend, I always tell them that they could get more from someone else if I think it's the case. If it's a stranger, I will also tell them this, depending on the circumstances. The answer is almost universally, "I don't care. I want it gone."
The internet is a strange place and you should have anticipated some of the responses here. Enjoy the car!
