Looking at a flight in the spring from FNC to LIS. They want €50 to add a 23 kg bag at booking.

That's in addition to paying for a higher ticket for a cabin luggage, standard carry on roller.

They also offer up to 26 kg for €54. I don't think I'd need the extra weight but my understanding is that they charge by the kilo when you check in bags and they find that you're over?

Since they price the ticket in such a way to make the fare jump considerably for luggage allowance, I'm guessing they enforce that at the airport and any extra kilogram will be charged at a much higher rate.

But it's all still much cheaper than TAP for the same date and approximately the same time of day departure.