Spirit, which filed for bankruptcy protection last year, says it has rejected the new Frontier overture but would be open to a higher offer.

Denver-based Frontier Airlines says it’s ready to keep talking after bankrupt Spirit Airlines rejected its offer to merge.

No-frills, budget airlines often lead the industry in customer complaints, according to government data, so if one were to disappear would it be missed by travelers? That is a question U.S. regulators will be asking after Frontier Airlines said Wednesday that it wanted to buy Spirit Airlines,