Tim, collecting cast iron cookware is a hobby of mine.....there is lots of good advise in the above posts.
But, I would like to kick in my 2 cents.....First off, there is nothing "wrong" with modern day Lodge. It will and can serve you well....in fact, I own serveral pieces of modern Lodge, mostly Dutch Ovens. But, it doesn't hold a candle to "vintage" cookware such as Griswold, Wagner, Favorite, Wapak, Vollrath, etc. (Or for that matter, older Lodge). Modern Lodge cast iron is MUCH heavier and more roughly cast than the older said pieces. And as a side note, when it comes to the garbage being put out by Emeril, Bobby Flay, or any other celebs....FORGET IT...made in China CRAP!!!!!! Cheaper? YES....but take your chances with that stuff....it's probably made from a '56 Chevy engine block mixed in with some lead and other questionable materials.
The older stuff is fairly easy to get....your best bet is a flea market....antique malls are an option, but be prepared to pay more, unless you get lucky. Ebay, is of course, another option, but I say forget it....when you tack on shipping, it's hardly worth it, and unless you know what you're buying, you're likely to pay too much. Estate and garage sales are also options, but unless you're hard-core collecting, they're a waste of time and gas.
Go to Wally World and look at Lodge...then go to a flea market and look at older stuff....you'll see the difference I'm talking about...it's worth it!!!
Have fun!