eBay Guides - American Girl vs. Generics - a Mom's Saving Guide
I have researched this myself. Our Generation dolls are, imo, your best bet. They're from Target. They come in deluxe version, about $34, which come with books and a few accessories, and a simpler version with no book and fewer accessories for about $22. Target also carries a decent line of accessories like beds, salon chairs, a horse, extra clothes.
Walmart carries their own version. I don't remember the name but I really wasn't impressed with the appearance. I think they're a couple bucks cheaper.
You can find the 18" Madame Alexander dolls at Sears. I saw them there a few days ago. They were cute but thier faces looked weird like a porcelain doll (look up madame alexander to see their expressions) and if I remember right they were quite a bit more expensive. If your kid is looking for a AG doll, she probably won't go for MA because of the huge difference in facial appearance. The Target and WM dolls at least look like a normal kid doll.
What you're looking for is an 18" doll. If you want extra clothes and accessories, you can find them all over the place and that 18" is kind of the key because pretty much all clothes for that size of doll are interchangeable. I found some on etsy, ebay and craigslist.
Good luck in finding something. My girls wanted an AG doll but my oldest has changed her mind. My 6 year old has been unwaivering. I wish she wanted a historical doll but she wants one that has the same eye and hair color and hair style as her. We're going to order her one in the next couple weeks.