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

Return flights

27 Sep - 05 Oct	Frontier Airlines
21 Sep - 23 Sep	Frontier Airlines
24 Sep - 27 Sep	Frontier Airlines
24 Sep - 28 Sep	Frontier Airlines
16 Sep - 29 Sep	Volaris	direct
21 Sep - 23 Sep	Frontier Airlines	direct
27 Sep - 05 Oct	Frontier Airlines	direct
17 Sep - 23 Sep	Frontier Airlines
17 Sep - 22 Sep	Frontier Airlines	direct
17 Sep - 23 Sep	Frontier Airlines	direct
17 Sep - 22 Sep	Frontier Airlines
24 Sep - 28 Sep	Frontier Airlines	direct

Also check the deals for one-way flights from Seattle to Guadalajara 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 Guadalajara in September from 312€

Return flights