Possibly by saving money from three or more years of a salary which is at or above the median wage for workers in the USA?
Alternatively, through having established a decent credit rating from utilising and paying off consumer debt over a period of years and then borrowing on the basis of that credit rating?
Less desirably, from borrowing from friends and relatives. Or bank robbery, for all I know.
My program had internal moonlighting, and most residents could cover ED shifts as well (as long as they’ve rotated there). That paid entirely for my applications and travel, which definitely wasn’t cheap!
You can also help to control costs by applying to nearby programs (if there are enough) and driving there, staying with friends rather than a hotel (if not covered), etc...
You should be able to swing fellowship interviews and flights on a resident salary. Worst case scenario is you put it on a credit card and pay it off later.
You paid for residency interviews when you made 0$. Most people do fewer interviews for fellowship and you make money now. Save some plus use the same tricks as apppying to residency like staying with friends or opening a mileage card with a big bonus to pay for a few of the flights.