I have a few cast iron pieces.
Amazon.com is a good place to buy cast iron online, as they offer free shipping over $25 if you buy from Amazon. Their prices fluctuate so if something is too high, check back and it's likely to go down. I've gotten some great deals there.
I have a vintage round griddle with bail handle that's about fourteen or fifteen inches in diameter. I use it as a pizza pan and it's perfect for that. Not only do we get that great crispy crust cast iron cooking is famous for, but it keeps the pizza hot so you don't get cold pizza when you come back for seconds. I know it's over 100 years old because it has a gate mark on the bottom where the molten iron was poured into the mold. That process was abandoned around 1900. I got it at a garage sale for $1.50, so it's possible to get great deals if you're patient. I also picked up a #10 Lodge camp oven for $2 at a sale, and a #12 unmarked Lodge camp oven for $8. My mom bought me the square Griswold frying pan hanging on the wall in the photo at a sale for 25 cents. The huge pan above it was bright orange when I got it and I paid $2 for it. I picked up a small Griswold griddle for fifty cents. The deals are out there!
Also keep in mind, well-cared-for cast iron will outlast you, your kids, and your grandkids. Well-seasoned cast iron is non-stick, and the seasoning is renewable and does not give off any sort of toxins since it's made from food-safe oils. It's a far better buy than cheap non-stick or even expensive non-stick pans because it will last forever.
If you see rusty cast iron at a sale, don't be afraid to pick it up and refurbish it. There are numerous ways of doing so. I love using electrolysis as it's easy and requires little effort on my part. Just make sure the piece is not cracked or warped and that the rust is surface rust, not metal flaking off.
If you want to get started with cast iron and can only afford one piece, I would recommend the Combo Cooker by Lodge.
It's not only two pans in one (chicken fryer and skillet) but it can be used as a camp Dutch oven outdoors or on the hearth. It even makes a great pizza pan! I don't own one but I demo'ed how to make pizza and biscuits in one for some camping friends who have one, at their campsite. The price is quite reasonable and because of its versatility, it's a great do-it-all set to start out with. Amazon carries it for around $35 with free shipping.
I know this sounds like an ad but I do know what I'm talking about! :ack: