Square skillets are almost always listed for $100 or more on eBay, as either a starting bid price or a buy-it-now price. But there is little indication of whether they are actually selling at that price. Here is one that should be interesting, an auction for the 11″ (larger size) square skillet starting at just $9.99.
If you are looking for a square skillet, this is a great one to bid one. It will be interesting to see what it ultimately sells for.
Here is another square skillet starting at a very low bit (although this one has no lid).