And I can't imagine that the kind of devs who can work on rendering engines come cheap either.
Back when I used to hack on the low-hanging Blender fruit my impression of the core devs was they did it for the love of doing it, any one of them could've gotten a job paying a lot more but they always stuck around because they liked it. And that was when they could only afford a couple fulltime devs who I imagine weren't making a whole lot.
Also, they couldn't pay anyone enough to mess with the spaghetti code of the old builtin renderer...
Edit: I can't remember the details but I vaguely recall Blender 2.8's headline new realtime renderer EEVEE was a by-product of a GSoC project, or something along those lines.
So maybe more like €48k gross for devs?
I guess their accounts are out there somewhere?