Holiday-Inn Express Madrid airport.
50$/night (37 EUR) for a good part of the year.
Including free breakfast.

Many cheap IHG properties in Madrid.
Some were (are?) also available using the 2-4-1 rate.

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There's also a Holiday-Inn somewhere near Warsaw that offers advanced rate of less than 50$ on specific days - and not much more on different days. But I can only assume it's a bit of a hassle to get to that property for a mattress run.