What he said. Flexible plastic conduit is pretty reasonable and if CAT5 gives way to CAT6/7/8 or fiber-optics, you can pull out the old stuff and use it to pull the new cables.
Would agree, put in the conduit and only the wire for what you need today.
I have also considered using the light weight black plastic water line in place of the conduit and drop it into a standard blue plastic switch box. Main thing your interested in is a way to fish wiring from one point to the next.
That approach would be more work but might save some money.