Aluminum foil and masking tape is a cheap option, far cheaper than enough yogurt to coat your windows, but in some places your neighbors might suspect you're running a meth lab.

Foamboard insulation, like they put under some types of siding, is cheapish and can be cut to fit inside a window frame easily. Bonus points for being easy to remove and replace.

You can find rolls of the same bubble material they make car sunshades out of for probably less than the gallons of yogurt this would require.

And as others have mentioned blackout curtains, awnings, chalk, window markers and paint all exist.

All of these things are probably going to be more effective, and most importantly SMELL much better, than using yogurt.