What is the approximate return on investment of a patent?

It depends on the content of the specific patent.

Some practical models can benefit hundreds of millions of people. For example, in the case of patent infringement dispute between Zheng Tai Group, a private enterprise in China, and Schneider, a world low-voltage electrical appliance giant, the amount of compensation for patent light infringement involved was10.50 billion RMB.

But some patents are worthless at all, just for administrative needs or other reasons.