$20.
I took it camping, built a huge fire, then put the skillet in it to burn off ALL the patina or anything else one it. Then took it home, put it in the oven and did a clean cycle.
Then started seasoning/building up my own patina. I wash it in the sink with soap and water sometimes.... I only paid $20 though so if I ruin it's no big deal. No problems yet and it always works fine.