If you choose to go with the real one --and as others say, they are much better made than the "knockoffs" -- Your daughter is old enough to earn it!
I'd set her some chores beyond her usual ones and pay her for the extra chores with the understanding that that fund is her contribution toward the doll. You might want to have her pay only part of the total cost and say you'll contribute the rest once she has reached her contribution amount (something a bit challenging but doable in a decent time, for instance, $25 earned over two months at a buck or two per special chore....She will say at first that that's way too much money for her to earn but you can sit down with her and show her on a calendar how long it will take, etc.)
The doll will mean much more to her if she earns it. You could even have her decorate a special container to put her earnings into as she gets them. Then have a celebration when the day comes and the doll finally arrives. I spent a year earning a doll by cleaning bathrooms when I was a kid, and I have never forgotten the lessons that earning the doll taught me. Since your daughter is only 6, I would be sure that your goal for her earnings is a realistic one and that the time frame isn't very long, but she is definitely old enough to learn to earn!