Although a serious collector may disagree, $100 is my limit for just about any cast iron any piece. Even then it has to be a larger Dutch oven or skillet that I can use to feed a hungry crew of railroaders.
Any cast iron in my modest collection is going to be put work. I don't collect cast iron to use them as show pieces. Each will be used to cook great meals, whether it's for personal camping or for large groups.
I'd love to own this 20-inch Griswold cast iron skillet. But it's current $340 price tag takes it out of my league. Bid if you must, but I suspect that the final selling price will peak at over $400.
All I can do now is watch the auction and dream of the day that I locate an Lodge 20-inch skillet. Although Lodge stopped making the round skillet several years ago, I see them advertised from time to time. I will break my $100 rule when I locate one.