There's a few questions in there, so I'll address them one by one.
What does A x B : C Mean?
Read this as A instances of a B number of inputs to C number of outputs. What you are looking for, if I understand correctly, is a 16x2:1 or a 32x2:1 chip. If C is more than 1, then your chip is significantly more complicated - you would no longer be selecting one input and connecting it to the output. Which leads well into the next sub-question -
Why are there $200+ chips for this simple function?
The specific part you linked is a 1x32:16 wide-bandwidth, DC coupled, buffered, video MUX, which can select any of it's 32 video inputs and output them simultaneously on it's 16 buffered outputs, with a gain of 1-2x. You could sorta think of it as a 16x32:1 with a lot of features. It's got quite a bit more inside than just CMOS switches. It isn't really designed for your function, which is...
How do I connect two memories to a master CPU
The most common method for hooking up multiple memory chips to a driver/controller/cpu is to use a tri-state bus. The address lines drive both chips, and the data bus is shared between all chips. Both chips should have a pin like "output enable", which can be controlled by the CPU. I found this article discussing memory buses at a rudimentary level - it has descriptive images. See Figure 8 for the gist of what I think you want. It is the simplest way of hooking things up, and the way I would recommend if the chips support it.
How would I make one?
Well, I think you were on the right track. CPU buses can be bi-directional, so intercepting the right output enable signal may be risky. The part you were probably looking for was a digital switch, something like this 16x2:1 FET mux. This is the cheapest one at $1.75 each. Wide bidirectional buses are best handled by ICs.
Note
I would check with the maker of your CPU to look for app notes and reference designs regarding memory buses. That will be the easiest way to see if you're on track.
I'd consider using analogue switches to do this - they are used extensively on switching thermocouples in and out of circuits and thermocouples are very low level signals. For example, the DG409 is used in this type of application and is specified in the brochure for audio routing applications. They are low power devices too. They can operate with a single +5V supply or from +/-5V supplies to +/-20V. The DG409 has two 4:1 multiplexers meaning you can route your signal to one of four places or choose on of 4 signals to route to a single place. This type of analogue switch comes with different switch configurations such as changeover or normally open too.
Best Answer
Uso 4066 analog switches. These make perfectly good audio analog switches (See This) and have been used even in high-end audio (my old Quad 44 preamp uses similarily specced chips). These have been around for a long time and there may be better moderen equivelents. You would need a good few to build up a large matrix but they are easy to drive from ttl/cmos, 5v/3.3v etc.