IDK, Ryanair in Europe (an epitome of low-cost airline) has both decent margins and zero crashes. They once had a birdstrike, hardly caused by their ticket cost, and wrote off the hull (no fatalities); otherwise, nothing.

A lot depends on your overall marketing. The airline can make money on a "stupid tax", e.g. people who didn't check twice the max. allowed weight of their baggage and have to pay a 100 USD/EUR fee for that single extra pound. I have seen it more than once.

People being people, you can almost rely on this happening frequently enough.