(Corrects price of shares in second paragraph)
MEXICO CITY, Oct 20 (Reuters) - Billionaire Carlos Slim's financial holding company Sociedad Inmobiliaria Carso is planning a $489 million offer to buy the outstanding shares of its real estate unit Inmuebles Carso, according to filing with Mexico's stock exchange on Monday.
Inmobiliaria will offer to buy the 441.3 million shares at 15 pesos per share, making the offer worth up to 6.62 billion pesos ($488.74 million).
Inmuebles Carso first announced that Inmobiliaria would buy its 19.55 percent oustanding shares in July. (1 US dollar = 13.5450 Mexican peso) (Reporting by Christine Murray)