Got a foil a while ago, and dropped a buck and a half out of money I gotten from cards I had previously sold for the same foil significantly under market price. Might end having to not gain as much as I had hoped on them, but still, I didn't actually spent my money on it anyway, just a bit of opportunity cost. I should be able to at least regain the costs anyway. :p
Basically, selling a bunch of cards (and a few TF2 items I had), I managed to get a bit over 5 USD.
On another note, I think I'll hold my sale cards until a week or two after the sale. Fresh enough that people might still be looking to get the badge, but old enough so the prices goes up a bit. Maybe a staggered release to minimize risks a bit.