Allegiant Air said Wednesday it has completed its purchase of Sun Country Airlines, finalizing a deal that combines two low-cost carriers at a turbulent time for the budget airline industry following the recent shutdown of rival Spirit Airlines. Las Vegas-based Allegiant said the transaction closed after receiving required regulatory and shareholder approvals. When the deal was first announced in January , Allegiant said it was valued at about $1.5 billion, including debt. “Today marks a defining moment in Allegiant’s history as we officially join forces with Sun Country,” Allegiant CEO Gregory Anderson said in a statement, adding that the new combined airline is positioned to offer broader access to affordable travel. Allegiant Air said Wednesday it has completed its purchase of Sun Country Airlines, finalizing a deal that combines two low-cost carriers at a turbulent time for the budget airline industry following the recent shutdown of rival Spirit Airlines.…