Last Friday I paid £43 for Manchester to Porto return Wednesday to Wednesday. Bit of a gamble at the time but I was willing to write it off if the game took place elsewhere.
Same flights are now £350.
I didn't fancy waiting around until the Wednesday coming home though (we *might* not win), so booked Faro to Liverpool on the Sunday night yesterday. Got it for £35 and I think its now £50, Train there is €29. Only issue with that is a 7 hour train journey with a 10 minute change in Lisbon, and if I miss the connection I'll miss the flight. Another gamble but I'll hang around Lisbon until the Wednesday before flying back from Porto as originally planned if that happens.
Unless you're willing to do a bit of traveling within Portugal or go for longer, at this stage you're going to struggle to do this cheaper than with Spike or the clubs partner. Day trips should land in Portugal before 9am so a good bit of time to explore, and most will have the bank holiday to recover.