what do you mean exactly ? I just wanted to say that it was an investment because I did not work as a contractor or employee while creating apps. But in a sense, I could estimate the cost because for the first 8 months I was not profitable and have to use some money I've have in the bank.
You wouldn't say to someone who is making 200k with a cushy corporate salary and ask "but what's your time worth?" - it's redundant.