Rental cars are available (starting at just US$27 per day) :
Avis (228-051) Has a stand at the airport.
Budget (258-911; Aeropuerto Internacional Chacalluta)
Cactus Rent a Car (257-430; firstname.lastname@example.org; Baquedano 635, Local 36) Prices are cheaper than the chains.
Hertz (231-487; Baquedano 999)
Klasse (254-498; www.klasserentacar.cl; Av General Velásquez 762, Local 25) Also cheaper than the chains.
Local buses and taxi colectivos connect downtown with the main bus terminal. Taxi colectivos are faster and more frequent. Destinations are clearly marked on an illuminated sign atop the cab, and fares within town cost just US$0.50.
You can rent decent mountain bikes with double shock absorbers at Bicircuitos (Estación Ferrocarril Arica-La Paz) for US$13 per day or US$4 per hour. Also inquire at Parinacota Expeditions.