It really depends. Series 1 and 2 only had one full set of 6 (if that) with lots of extra parts, so the basic sets go for more. Hoth Leia and Amanaman were short packed AND chase boxes, so they command a little more money as well.
With S3 and S4, they have 2x of each figure and part, so a box with no chases nets you two BAFs and 2 basic sets. Even if you get a chase, you still get the right BAF part, which is pretty nice. I bought two boxes of S3 and sold my three extra basic sets for $80 each with free shipping. I saw sets go earlier for about $100, and you can now buy them for maybe $65 plus shipping? Having 2 of each figure really drives down the basic set prices.