Tesla Inc. plans to manufacture a car that will cost $25,000 in about three years’ time, fulfilling an elusive long-term objective to sell a cheap mass-market electric vehicle, Chief Executive Officer Elon Musk said Sept. 22.

Tesla Inc. will provide a highly anticipated technology update Sept. 22 when Elon Musk takes center stage at an event the CEO has dropped hints about for months — and which has helped propel the company’s sky-high valuation.