Nothing is free. You're paying for it somewhere. I hate it when services bake extras in because then I'm just paying for it whether I want it or not. "Free Hulu or Netflix. Free phone, blah blah."
Discussion
Open source is what?
Software source that's available to inspect (can be behind paywalls, actually, depending on the license).
I can see through your weak point though.
1. Open source doesn't mean the software has no cost. It's a broad term with many different licenses. Some make source available, but still have license restrictions that add a cost.
2. Free and Open Source (FOSS) is probably closer to what you actually mean. Those licenses don't require payment, but don't forbid it either. People can compile the software from source if they wish for "free" (it still requires resources and time), but that doesn't mean the software is free to build, host, distribute, or maintain. Some resource was expended for that software.
Open source isn't free.
FOSS isn't free.
Someone paid something even if you didn't. Often, it's people like me who send money to the developers and maintainers regardless. Or developers and maintainers who donate their time so you don't pay anything. They paid for you.