You said that if you can't get a good price now you might wait until their birthday but...AG does not do sales. Very occasionally there is a break on shipping prices or something of a "sale" on certain items they are pushing (or discontinuing) but for the dolls themselves -- don't expect to find some "after Christmas sale" deal. Won't happen. They know they can get whatever the asking price is.
And as others said, the dolls are worth the money if a girl is really going to play with them (they do last) and is going to take care of them. My daughter has two; one was a hand-me-down and is at least 20 years old, and the other is a newer one that was a gift. Both are well made. But for girls who are going to be pretty rough with the dolls, yes, the knockoffs might be better for the short run.
You didn't say your girls' ages but I would really reserve these dolls for girls at least, maybe, eight and up, depending on the child; some kids really wouldn't look after them until maybe 10 or so. We live near one of the AG stores and I see girls who are clearly as old as perhaps 12 to 14 in there with their dolls in their arms!
You can save money on the clothes for sure. Many people have begun online or local businesses making clothes to fit AG dolls and there are lovely things out there for a good bit less than the official AG clothes. Search online and at craft shows. At a craft show recently, ,my husband bought a gorgeous kimono and a jeans/top set for my daughter's dolls for Christmas and paid at least $10 less per outfit than I know he would have paid for comparable clothing at the AG store or online. (Similar AG outfits would have been probably $22 to $28 while he paid about $15 per outfit.)