(Adds earlier price range, underwriters, background) March 31 (Reuters) - Frontier Group Holdings Inc was valued at $4 billion after its shares opened 2% below their offer price in the low-cost carrier’s market debut on Thursday. The stock opened at $18.61, compared with the offer price of $19, which was at the lower end of its $19 to $21 indicated range. The company sold 30 million shares in its initial public offering for a raise of $570 million. It plans to use part of the proceeds to repay some of the $150 million in government loans it took under a COVID-19 relief package. The listing comes as U.S. airlines begin to emerge from a pandemic-driven crisis, with domestic leisure travel-focused carriers such as Frontier poised to benefit from a quick rebound thanks to the rollout of COVID-19 vaccines. Another budget carrier Sun Country Airlines, backed by Apollo Global Management Inc, made its market debut earlier this month. Denver, Colorado-based Frontier, owned by private equity firm Indigo Partners, turned cash flow positive in early March, Chief Executive Barry Biffle told Reuters. The airline flies to more than 100 destinations in the United States, Mexico and the Caribbean and operates 100-plus Airbus A320 family aircraft. It averted employee furloughs during the pandemic and was among the first to announce pilot and flight attendant hires. Citigroup, Barclays, Deutsche Bank Securities, Morgan Stanley and Evercore ISI are among the underwriters for the offering. (Reporting by Niket Nishant in Bengaluru; Editing by Aditya Soni)