A few people have asked where and how to get started. If you’re lucky enough to have a relative or friend who has an older seasoned skillet who will give it to you, take it. Seriously the best. Otherwise, try to find a flea market or check yard sales. You may be able to find a piece of good used and well-cared-for cast-iron there.
However, since this isn’t a usable answer for many people, I thought I would suggest you consider purchasing cookware from Barbara and Doyle Bailey who run The Cast Iron Cookware Shop. When I needed a few pieces to be able to work on the cookbook, I did some research and found them. I was impressed with the variety, the price, and the customer service. It was surprising, but I was happy with every item I purchased from them and was delighted with the personal responses I got from them when purchasing cookware.
If you’re trying to decide what you should purchase first, I would suggest getting a 10” or 12” skillet to start with. If you’re most likely to only cook for 1 person, you could get the 8” skillet. I have 2 10” skillets that are round, 1 10” square grill pan, 1 14” skillet, and 1 4” skillet. I have two Dutch ovens, muffin pans, loaf pan, corn stick pan, and a grill grate for using on our grill. This is all I used to write every recipe in the cookbook, but most of the recipes were made in the skillets. I love them. I think you might, too.