My experience with Goodwill, at least in my area, is that pretty much everything there is total garbage. I'll mostly see modern-day dirty used Lodge skillets for close to the asking price for new on Amazon or at Walmart or Target. Or, occasionally made in China or Korea pieces such as Benjamin & Medwin, or some enameled piece (almost always not Le Creuset) that looks like it's been though WW3. They usually put the good stuff up for auction online and/or employees grab it for themselves to keep or resell. YMMV and this definitely depends on where you live.
I did recently see a Finex at a Goodwill. Looked totally destroyed, the cooking surface was all pitted up and I'm not even sure how someone managed to do that to a new $200 skillet. The price tag was over $120, no thanks.
Most of what I'm able to find that is worthwhile is via yard or estate sales, and occasionally in thrift shops. Antique malls every once in a while, but these days they are generally onto the value of the marked pieces (especially the larger logo Griswolds) and so the prices will be comparable to what one would find on eBay.
Occasionally, I can find a great deal locally on unmarked or pieces where they don't understand the markings to know what they have. I personally love when I manage to find crudded up pieces, because most local sellers tend to not understand what they have or perceive the crud and/or a bit of surface rust makes the piece not worthwhile. Got a nice single notch Lodge this way semi-recently.
Btw, you can do searches online for local estate sales and get alerts sent to you.
Happy hunting.