AirHint found the following cheapest return flights from Austin (AUS) to San Juan (SJU) in September 2025 (see full year).

Return flights

11 Sep - 15 Sep	Frontier Airlines
26 Sep - 29 Sep	Southwest Airlines
06 Sep - 18 Sep	American Airlines
05 Sep - 07 Sep	Spirit Airlines
15 Sep - 29 Sep	Spirit Airlines
05 Sep - 08 Sep	American Airlines
11 Sep - 16 Sep	Southwest Airlines
05 Sep - 11 Sep	Spirit Airlines

Also check the deals for one-way flights from Austin to San Juan 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 Austin to San Juan in September from $211

Return flights