Question : Have you considered flying out of an airport besides Tegel Airport (TXL)?
Answer : Departing from Tegel Airport is not the only way to get to Porto Airport. Try looking for flights from Berlin Brandenburg Airport (BER) as well. Over the next few months, flights from BER to OPO are being priced 13% cheaper than flights from TXL to OPO. Being only 16 miles away, it's easily accessible for most.