Hmmm Samantha still holds her value and is available direct from AG so she's still valued around $80-120. You'll spend more on an older one with a white body. Also she was retired previously so there are quite a number of releases for her.
I have one but I have a number of outfits and such for her so I will be asking $120.
If you want to find a cheap AG doll, you have to troll through thrift shops and look on Ebay for dolls that aren't identified by their character - "Brown hair brown eyes doll" will probably find you a ratty Sam that has to go to the Doll Hospital which will run about $50-80.
Best of luck!