They are all hard to find, as you will know
I think some are more sought after than others - June, July, August, October, December - maybe its because they are all very special colour combos or maybe those are just popular birth months/favourite months, I am not sure. I think some of the others pop up less than August but are not quite as desirable, if that makes sense.
If she is in nice condition with no issues - anywhere from $180-200.