Cambridge, MA-based biotech drug maker Genzyme (NASDAQ:GENZ) and its big pharma suitor, Sanofi-Aventis, are still far apart on price. Paris-based Sanofi said today that it is extending its tender offer of $69 per share or $18.5 billion for Genzyme until just before midnight on February 15. The previous offer deadline expired on Friday. Sanofi so far has not upped its offer since its pursuit of Genzyme began during the summer. And the French drugmaker says that, though it is in talks with Genzyme, “there remain significant differences” between what Genzyme thinks it is worth and Sanofi’s offer.