There are now five different products from Canon in the 70-200mm L lens family:


70-200 f/4


70-200 f/4 IS


70-200 f/2.8


70-200 f/2.8 IS


70-200 f/2.8 IS Mark II


(I left off the L and USM initials, but they apply to all five lenses.)


Ignoring the Mark II, changing from f/4 to f/2.8 costs $500-600, and changing from non-IS to IS costs $500-600.