I wanted to give a quick update on this topic. (The other answers with prices are kinda outdated).
Same as the other answer a kilobyte of data is 640k gas.
But in contrast to two years ago the gas price is now ~10 gwei instead of 50 gwei.
However the price of ETH also increase.
Two years ago it would cost you $0.076/KB.
Nowadays it costs you $1.204/KB.