AirHint found the following cheapest return flights from Bilbao (BIO) to Sofia (SOF) in September 2025 (see full year).

Return flights

25 Sep - 27 Sep	Vueling Airlines
09 Sep - 16 Sep	Vueling Airlines
08 Sep - 16 Sep	Vueling Airlines
03 Sep - 09 Sep	Vueling Airlines
22 Sep - 28 Sep	Vueling Airlines
19 Sep - 28 Sep	Vueling Airlines
02 Sep - 09 Sep	easyJet
26 Sep - 28 Sep	Vueling Airlines
01 Sep - 07 Sep	Vueling Airlines
02 Sep - 06 Sep	Wizz Air Malta

Also check the deals for one-way flights from Bilbao to Sofia 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 Bilbao to Sofia in September from $117

Return flights