Some people claim and that it's not possible to season these bumpy pans properly. I don't buy it. I have compared my shiny, totally smooth 1930s
Griswold (acquired at a flea market) to my 10-year-old
Lodge skillet (which I bought new and seasoned myself). The old stuff is certainly more non-stick, but the new Lodge pan is pretty darn close, and good enough for most needs.
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If you're lucky enough to come across a reasonably priced cast iron pan from the early 20th century at a yard sale or flea market (say, under $50 or so), scoop it up immediately. You can occasionally also find good deals on eBay and sites like it.
I personally find it ridiculous to pay the $150-plus that some sellers are asking for old cast iron when a new cast iron pan, like the cast iron skillet from Lodge costs a mere $16.00 and will give you an equally lustrous nonstick surface with just a bit of time and care.