What is the simplest device for measuring the power consumption of appliances?

Question

Electronics

What can be purchased inexpensively (options from ebay, aliexpress and dx are welcome) to measure the electricity consumption of appliances (kettle, air conditioner, etc.)? Ideally, it should show not only the current energy consumption, but also skillfully calculate the amount (for example, from the moment the kettle is turned on until the moment it is turned off).
upd . Apparently, something like this - habrahabr.ru/post/152449 - but I want it cheaper (5 dollars).

Answer 1

Wattmeter. On eBay from 500 rubles. But not like this!!! economenergo.bm360test.ru