AirHint found the following cheapest return flights from Seattle (SEA) to Mexico City (MEX) in September 2025 (see full year).

Return flights

23 Sep - 04 Oct	Volaris
27 Sep - 12 Oct	Volaris
27 Sep - 11 Oct	Volaris
27 Sep - 10 Oct	Frontier Airlines
19 Sep - 28 Oct	Volaris
27 Sep - 13 Oct	Volaris
19 Sep - 22 Sep	Volaris
19 Sep - 29 Oct	Volaris
25 Sep - 02 Oct	Frontier Airlines
15 Sep - 24 Sep	Volaris
24 Sep - 06 Oct	Frontier Airlines
18 Sep - 23 Sep	Frontier Airlines
11 Sep - 22 Sep	WestJet
12 Sep - 17 Sep	Frontier Airlines
11 Sep - 15 Sep	WestJet
13 Sep - 15 Sep	Frontier Airlines
12 Sep - 15 Sep	Frontier Airlines
11 Sep - 18 Sep	WestJet
12 Sep - 16 Sep	Frontier Airlines
27 Sep - 10 Oct	Aeromexico	direct

Also check the deals for one-way flights from Seattle to Mexico City 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 Seattle to Mexico City in September from $376

Return flights