I obsessed over these pans for quite a long time . I've bought and sold a bunch and finally settled on Erie second series pans. Ebay is the best place to find the pans and generally speaking is also the marketplace that sets the price for these pans. There are several great makers and a lot of history and the more you know, the better pans you can buy for cheap. The Wagner Griswold society is the place to go to learn a lot about these pans and the society page is pretty insane. This is a page on the history of Erie (which later became Griswold) that I found to be really useful:
http://www.wag-society.org/guest/ERIESkilletArticle.pdf. The iron ore used for these early pans is - for what ever reason - very different in structure from the ore available today. It is almost too hard to file which is saying something. The earlier pans were made as light as possible but reinforced in the areas that often fail if dropped ,like the handle ,and the lip. This 100 plus year old cast iron is hard ,brittle, tight grained, takes to seasoning much quicker than todays pans and is also smoother as some have noted. The pans were marked with model and the maker's mark. Here are some things I have learned the hard way:Getting the best pans cheap takes some work. You have to know what you are doing. The factors that drive up the value are rarity, vintage, type, makers mark, condition, seasoning and the quality of the ebay ad (ie notes and photography). Rare pans cost a lot - several hundred dollars more often. Some series and Companies draw a bigger price from collectors but are not better for cooking in any way. For example a really nice third series Erie will tend to be more than a second series Erie but there is really no functional difference. Erie's tend to be a lot more than Wagner's but are not superior in quality except in subjective ways. Some important saving tips: When looking for pans search "cast iron skillet" and a number and that will pull up the most pans usually. The number tells you the size. 5-12 being the most used sizes and 8 being the most produced/popular and usually cheapest size. The pans get bigger as the numbers go up and yes there are pans smaller than 5's and bigger than 12's and all sorts of other vintage cast iron wear. There are a lot of great makers with less name recognition that will often go for less and are slightly different in their characteristics. If you are looking for a number 5 for example (the perfect 1 or 2 person pan and everyone should have a 5 or 6) You might try looking for these maker's: National,Sidney, Pique, Favorite, Marion, Wapak, and Martin to name most of the ones I know and have seen. Nationals look just like early Erie's but tend to have shorter sidewalls. Favorites on the other hand tend to have the tallest sides for a given size (so less splatter) but are a bit heavier than Erie's. Sidney and Wagners are usually the same style and were related companies. Another tip: there are three defects that are really helpful: 1.Pitting in the bottom will bring the price way down but not effect the function because collectors don't want pitting.2. A pan that does not sit flat and has a slight wobble may be a good pan if the cooking surface is just slightly concave but that is the kiss of death for collectors. When a pan is heated and the metal expands most cast iron pans rise up a bit in the middle so if they start out concave they become closer to flat when hot. If the surface starts out dead flat, when heated they become convex (which I don't prefer because the oil (used to brown or saute) drifts off to the edges of the pan. Sizes 7-10 seem to be the most effected in my limited experience. A pan that is concave or just a little concave cooks best for my taste. I usually ask people to put a half cup of water in the pan cold and tell me where the water runs to. I would recommend that you avoid pans that have a convex cooking surface when cold. Last nickel plating! Some pans were nickel plated to sell to wealthier clients and cost twice the price of a non-plated pan. The best pans were taken from those cast, and then plated. After 100 years the plating is usually worn badly and the pans look bad, so the price is low, but underneath, the pan is usually sweet! To remove the nickel you just need to find someone who does plating - say chrome plating - who will work with you . They will have vats of chemicals that will remove the nickel. Applying nickel is often the first step in chrome plating and what you can plate you can also un-plate. and I found a guy who did this for 10 bucks a pan while I waited!
Obviously, I could go on and on but my last few points: Many pans need a good deal of clean up when you get them and pans that are photographed poorly can often be a bad surprise. I find the pans photograph best in natural sun light so look for ads photographed that way to get the best detail. Cleaning the pans is messy at the least and dangerous at the worst. Two methods I find work: Spray pan with oven cleaner and put in a plastic bag overnight to give the cleaner more time to work. Then remove and scrub and do wear gloves and an apron. This works for pans that are merely dirty. For more stubborn pans, baking a pan in the oven at 500 degrees for an hour or so will cook off a lot of stuck on stuff and just turn that residue into a black powder that can be wire brushed or wet sanded or carefully filed off. Caution this could be smokey and do not take the pan out until it cools. Regular oven mitts are not good enough to grab a pan this hot. Or you can look for sellers who have their pans cleaned before the sell. And buyer beware. Avoid pans with cracks, bad photos, or one photo. There are lots of fake pans and knockoffs and some of those are also 100 years old. You have to read up to avoid things like sprue marks on the bottom of a pan (a sure sign of a bad counterfeit). One more thing... a good article on seasoning a pan:
http://sherylcanter.com/wordpress/2010/01/a-science-based-technique-for-seasoning-cast-iron/. Did you know that Flaxseed oil (bought at healthfood stores) and Linseed oil (bought at the hardware store) are the same thing? Except that the later may have driers added to it that will kill you if you eat it or season your pan with it. Cheers and sorry for the long post. I am new so be gentle.