In Santiago, City Bike Tours offers tours starting at 33,000 and tour everyday. They have four different routes: Local Life & Markets, and Park and Politics Bicycle Tour, Mapocho Sunset Bike Tour, Full Day Bike Tour. All tours include bike, bilingual guide, mineral water and a map.
Location: Constitucion 153, Providencia, a 1o minute walk from the Baquedano metro stop. info@labicicletaverde.com. Reservations are required. According to their flyer they are recommended by Lonely Planet and Travel & Leisure.
Tour Expert Chile offer multiple tours (10 listed on their flyer), from cities to the mountains. Costs from 30,000-80,000. I had not read reviews but by they had a very polished website. reserva@tourexpertchile.cl