For 35" to 55"-wide windows, cheap plastic blinders only cost about $10. But that's for apartments or houses in bad neighborhood. You should use better shade/blind/drape, and $50 is really minimum, such as the shade (not plastic blinds) in 3rd floor link, if you have a decent house and want to keep the resale value. Sometimes you can find the pre-cut ones for deep discount, if they happen to fit the size of your windows.