tldr:
Costs associated with pilot training including classes, flight hours accumulation, and licensing will average around $80k. And most of the top airlines require or strongly prefer a college degree, so altogether a potential pilot is dropping $200k just to get a foot in the door.
But that is just to get a commercial license, they still need 1,500 flight hours before they can pilot for the big airlines like Delta. It'll cost another $130k to attain those flight hours if they paid for it themselves by renting planes, so they usually end up as flight instructors or skydiving pilots to get the required hours.
After all of that, a first year pilot can get hired by a regional airline with a starting pay of....30k.
The big bucks don't come until later.