Not a lawyer but seems like source projects would have a hard time showing damages since they don’t charge for the software.

I don't believe you need to demonstrate specific damages for a copyright infringement case in the US. You only need to demonstrate two facts: that you are the legitimate holder of the copyright, and that the other party did in fact infringe.

It's pretty funny that corporations can levy a multi-million dollar judgement against a single mother for pirating a CD, but then when the tables are turned, it's no big deal

As others have said, penalties are not related to how much you charge for the product itself. For example, when you start illegally distributing music your penalty won't be retail cost * number of copies. There's multipliers & things that get applied. Basically your judge/jury will figure out the damages amount after you're found guilty (assuming you don't settle).

This also makes sense when you factor in that retaining lawyer services to prosecute the infringement costs time and money (not to mention the court's time & resources to handle the case).

Suppose, I'm an author of GPL software. I think that my code costs $1M. I expected that if someone uses my software, according to license, then he will release his software under same license for me. Now, somebody used my $1M project in his $100M project in violation of my GPL license. My losses are $100M.

Has anyone successfully done this for GPL licensed software?