Figures from BrickLink: the lowest listed new price, the six-month average sale price for new and for used copies, and the six-month sales volume behind each of those averages.
Volume is how many sales went into the six-month average next to it. An average built on only a handful of sales describes a thin market, so treat it as a rough guide rather than a settled price.
A minifigure is marked retired when every set it appears in has retired.
Open the minifigure. Its page lists every set it appears in, the parts it is made from, and related minifigures from the same theme or subtheme.
Quick filters cut the list to exclusive figures, to figures above $50, $100 or $250 on BrickLink new, to those above $50 or $100 used, and to high-volume figures. Every price column can also be sorted from high to low.