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

Return flights

22 Sep - 26 Sep	Southwest Airlines
14 Sep - 17 Sep	Frontier Airlines
18 Sep - 22 Sep	Frontier Airlines
17 Sep - 23 Sep	United
19 Sep - 22 Sep	Southwest Airlines
17 Sep - 22 Sep	Southwest Airlines
09 Sep - 16 Sep	United
11 Sep - 15 Sep	Frontier Airlines
10 Sep - 17 Sep	Southwest 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 197€

Return flights