How to build an amplifier in less than 2$?

Refik writes “Why do we need Amplifiers? How to build a simple one? LM 741 – You have some output source (for example an analog sensor) where the voltage is very low, just few mV (millivolts), and you would like to measure the output with your ADC (Analog to Digital converter) and with the results do some calculations with your MCU (Microcontroller) or some other device. The values the ADC gives you are all almost the same because its bit resolution is too small to show you any differences between the different states of the sensor.” Link.