Airline travelers—particularly those who fly enough to earn elite status—used to have a reasonable chance of getting bumped up to business or first class for free if open seats remained at flight time. But free upgrades—and even frequent-flier upgrades—have become extremely rare or nonexistent. Examples: Delta has eliminated complimentary upgrades on most cross-country flights. United has eliminated them on “premium service” flights (such as those with flat-bed seats).

That’s largely because the airlines have found a new way to make money—selling upgrades. The upgrade price can be anywhere from $50 to $300 on a domestic flight, and it can top $1,000 on international flights. Some airlines, including American, auction off upgrades.

What to do: Choose flights that business travelers tend not to fly, since business travelers are more likely to spend cash and/or miles for upgrades. Low-business-travel flights include Saturday, Tuesday and Wednesday flights. If you’re told that frequent-flier-mile upgrades are not available, try again two to five days before departure—airlines sometimes make some additional seats available for mile upgrades during this window. Or if you are willing to wait to purchase a ticket (and risk paying a higher price or no availability), call the airline three to five days prior to your intended departure date and ask if there are any flights to your destination where frequent-flier-mile upgrades are available. If yes, book an upgradable ticket and immediately claim the upgrade.­