If Steam is taking 30% and uncle Sam is taking 35%, $500 is really $175. You need to earn roughly $1450 per-month to make around $500 per-month. Of course, that doesn't count any marketing/domain/asset/license/etc fees.
As per your math, you added them together… percentages like that are multiplicative since you wouldn’t get taxed on the fees paid to steam, so it’s really more like $227.50 in your example. Still less than half, but all your additional fees or whatever get deducted out of the big 35% bucket.
I have nothing but respect for people that do. I've dreamed of it. I could never pull the trigger though. I can't justify putting four to seven years in a game to make pocket change out of it.
Sure... the creative aspect is great. Having players enjoy it is great. But eating and keeping my house is pretty good too.
It sounds like this was a passion project, not something intended to replace a full time job, though.