Marx is thoroughly outdated. He didn't anticipate the rise of capitalist media with sophisticated propaganda techniques. He didn't anticipate the rise of secret services that are powerful enough to force regime changes anywhere in the world, including democratic countries. He didn't anticipate the rise of war profiteers and military-industrial complexes. All these things are real game-changers.
It's much better to read Noam Chomsky and Howard Zinn.
The easiest way to figure the cost of living is to take your income and add ten percent.