The big one: Travel out of season.

Doing this saves a massive amount of money. I am now on my way to the Italian Adriatic coast, where the weather is still around 22c/70f but the season has completely shut down.

I have booked a room at a 4* hotel with balcony and sea view. The price: $157 for 5 nights, including full breakfast and all taxes. That's not per night, that's the total.