The intel 4004 contained 2250 transistors. Already we are not in the millions. Now, each 7400 series chip contains 4 gates. Each gate contains at least 2 transistors (I am not sure the number, likely it is more) 2250/8= 282 chips.
Of course no one can reasonably simulate an i7, but older CPUs are more than possible. I believe you can actually get a kit to build your own (I think it was an 8086) about the size of a desktop cube. They even include adapters so if you have an old motherboard, you can plug it in. I want one of those, it would be cool.