It costs US$100 to renew a tourist card for 90 more days at the Departamento de Extranjería. Take with you photocopies of your passport and tourist card. You can also visit the Departamento de Extranjería in any of Chile’s regional capitals, which will likely be much faster than waiting in the hours-long lines here.
Many visitors prefer a quick dash across the Argentine border to Mendoza and back, rather than paying for a visa extension.
For questions about visas it's best to contact the call center which, unlike physical branches, has English-speaking attendants.