Try this calculator form the Financial Times to estimate the value of your user data when sold in large chunks of anonymous data. The more details, the higher the value of it. The outcome is extremely low. However if you try to sell your user data as an individual with identifiable records it may become quite valuable.

There are various companies buying user data with real money from individuals, like Handshake.

I took the next description directly from their website:

 Handshake is an app and a website that allows you to negotiate a price for your personal data directly with the companies that want to buy it.

Make sure to check it out. Maybe you want to get some cash for your user data. Please let me know if you sold it and how much you got paid for it. I personally would never sell my data like that and many of you may think alike. But perhaps you do fill in your information from time to time when there is some kind of reward or loyalty program, like a price contest.

Food for thoughts.