A United Airlines airplane and a Spirit Airlines airplane at Newark Liberty International Airport, New Jersey. Gary Hershorn/Getty Images Airlines are stepping in to help stranded Spirit customers after the budget carrier folded. United is offering price-capped, one-way tickets until May 16. American Airlines, JetBlue and Frontier have also reached out with offers of support. United Airlines is offering price-capped tickets to Spirit customers who have had their flights canceled following Saturday's announcement that the budget airline has shut down . "If you had a ticket booked on Spirit and your flight was canceled, for the next two weeks you can visit united.com/specialfares to find price-capped, one-way tickets from most cities where Spirit flew, including Atlanta, Chicago, Fort Lauderdale, Houston, Las Vegas, Miami, Newark, New Orleans and Orlando," United said in a statement. It said most of these special fares are capped at $199, with longer flights priced no higher than $299.…