Where did you find that the 4051 is only for digital. The name in he datasheet is clearly "8-channel analog multiplexer/demultiplexer".The CD and HEF versions are the 'original' versions from long ago; they work with supply voltages up to around 20V (check the datasheet if needed) also standard would be around 12V or so.The H in HC stands for "High Speed" and is the newer version; they were designed for 5V power supply (some go higher, again check the datasheet if needed).I have no idea about pricing.
Is 74 cents a good price?https://www.digikey.com/product-detail/en/toshiba-semiconductor-and-storage/TC74HC4051APF/TC74HC4051APF-ND/8705084067 not available in thru hole. Both are available in SMD.
how do I increase the number of analog input on the arduino, for example to control four stepper motor w/o driver, although I think I can't, since current won't be enough.
Why do you believe you need analog inputs to drive motors? The only reason I can think of is to monitor the motor currents. But only advanced drivers have that capability, and as a beginner I doubt you knew that. I suspect you have seen the A0..A6 pins used as digital outputs. And you are correct, they can't supply enough current to drive a motor, but you may have seen them connected to a motor driver chip or module.
@ compnaion If you are going to expand your analog channels of UNO, you have to use 74HCT4067 (TTL Level Logic) and is compatible with Arduino UNO which is also TTL Logic (VOH = 4.2, VOL = 0.9V).74HC4067 and CD4051 are CMOS Logic, and they are not compatible with TTL logic. For CMOS logic:(VIL = 0V to 1.5V). Therefore, UNO might fail to drive the selection bits of the CMOS analog multiplexers. The VOL (max) value for TTL logic (UNO) is: 0.9V.What does 74 behind 74HC4067 indicate? CMOS logic with TTL speed (low power high speed logic).
with the HC version, one is always safe.
So it's probably safe to use a 74HCT4051, but a 74HC4051 is guaranteed to work with the 328P in all possible conditions.
There is a chance that the 328P gives a Vol (at full load) that is in this 'forbidden' region. Now life is not that bad if you limit the current to a few mA; see fig 31-306 on page 479 of the 328P datasheet that shows that at lower sink currents the Vol is close to 0V.