[ZyanWu]

Well, it's a bit of a chicken and the egg, no? Microcontroller won't work without a (most likely) crystal oscillator or something to act as a clock signal.

Now that I think about it, no, it's not even cheaper as XTALs are quite pricy compared to other discrete components.

I didn't mean to be rude - I interpreted the comment as "Would you like to build an (insert random object here)? Well, you can just BUY it and be done with it" - may not be as I put it (dumb) but certainly... simplistic and purpose-defeating

[dgacmu]

I mean, yes, if you're designing a microcontroller you need a clock source, but from the perspective of implementing a circuit as a more normal designer, the UC has it already. And lots of small UCs have an internal clock source so you can omit the external xo unless you need a particular frequency, accuracy, or in some cases a precisely timed micropower sleep. For example, the sub-$0.10 32 bit PY32F002A can do 24MHz internally -- but I would bet it doesn't have great temperature compensation or other things you'd want for timekeeping or being a good frequency ref. (But you're not going to get that out of $0.20 of components anyway.)