AirHint found the following cheapest return flights from St. Louis (STL) to Cancun (CUN) in September 2025 (see full year).

Return flights

25 Sep - 29 Sep	Frontier Airlines	direct
10 Sep - 14 Sep	Frontier Airlines	direct
20 Sep - 26 Sep	Frontier Airlines	direct
08 Sep - 20 Oct	Frontier Airlines	direct

Also check the deals for one-way flights from St. Louis to Cancun in September.

The deals are updated regularly. The prices may go up as tickets are purchased by other travellers. Only the cheapest flights are offered. Select a price to book and secure these cheap prices.

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Cheapest return flights from St. Louis to Cancun in September from $243

Return flights