Airfares with flat-fee, low-cost upgrades at time of booking are fleeting. Here’s a big exception.
Last October United joined American and started offering enormous First Class discounts through EasyUp fares to Southern South America: upgrades from Business Class costing $500 to $2,000.
American, Nine Months Later
At press time, American is still offering low fares on the Miami-Rio de Janeiro route, starting at $4,453 in First and $4,035 in Business. In other words, the flat-fee upgrade at time of booking is only $209 one-way. (See screenshot below.)

United, Nine Months Later
United is only offering First Class service on its Chicago and Washington, DC- São Paulo routes.
United still offers low First Class fares with a $300 flat-fee upgrade one-way at time of booking, about $100 more than nine months ago. First and Business Class fares have increased. Now, First Class on Chicago-São Paulo starts at $5,878, Business Class at $5,278. (See screenshot and chart below.)

Lowest First Class Fares FCF Found to Sao Paulo on United
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EasyUp Fare Concept Remains Unchanged
Restrictions vary by route and airline; the fares are often valid year-round, but the bottom line is the same: The difference between Business Class and First is still unprecedentedly low—only $209 to $300.