There are no entry requirements for nationals of EU countries. Citizens of Australia, the USA, Canada and New Zealand do not need visas to visit France for up to 90 days. Except for people from a handful of other European countries (including Switzerland), everyone, including citizens of South Africa, needs a so-called Schengen Visa, named after the Schengen Agreement that has abolished passport controls among 26 EU countries and has also been ratified by the non-EU governments of Iceland, Norway and Switzerland. A visa for any of these countries should be valid throughout the Schengen area, but it pays to double-check with the embassy or consulate of each country you intend to visit. Note that the UK and Ireland are not Schengen countries.
Visa fees depend on the current exchange rate, but transit and the various types of short-stay (up to 90 days) visas all cost €60, while a visa allowing stays of more than 90 days costs €99. You will need: your passport (valid for a period of three months beyond the date of your departure from France); a return ticket; proof of sufficient funds to support yourself; supporting documents explaining your stay in France for an extended period; recent passport-size photos; a completed visa form; and the visa fee. Check www.france.diplomatie.fr for the latest visa regulations and the closest French embassy to your current residence.
Tourist visas cannot be extended except in emergencies (such as medical problems). If you have an urgent problem, contact the Service Étranger (Foreigner Service) at the Préfecture de Police for guidance. If you entered France on the 90-day visa-waiver program (ie you are Australian, Kiwi or American) and you have stayed for 90 days, you must leave the Schengen area for an additional 90 days before you can re-enter.