While there are still good deals to be had on eBay, it seems you have to look harder to find them than you did say 5 years ago. Back then, the daily average number of listings in Collectibles > Kitchen & Home > Kitchenware > Cookware > Cast Iron was around 4000. As of this writing, it's over 12,000. In a world where demand is constant, a jump in supply such as that should translate to lower prices, but we can see that in the world of online auctions, that's not the case. I can remember around that time buying a beautiful older Favorite Piqua #12 block TM outside heat ring skillet for $50, and a Griswold #8 Slant EPU heat ring skillet for $20, neither with any real bidding competition.
Out in the real world today, at least in the locales I search, it's all over the place. I still see bargains, I see things priced about right, and I see things that just make me laugh (rusty Taiwanese skillet $29, Griswold #3 SBL skillet $110 on sale for $75!). Our toughest part out there these days is the seller who looks at the ridiculous asking prices on eBay and thinks that's what things should or actually do sell for.