If you buy active monitors (stereo speakers which have a built-in amplifier) and an active subwoofer, you can just run them off RCA cables and a splitter.
I think some monitors have a passthrough on them, so you wouldn't even need a splitter - you would just have RCA cables from the back of your TV going to the monitors, and another set of RCA cables from the monitors to the subwoofer.
You need to be sure that your TV is capable of adjusting the volume of its RCA output though - some of them have a fixed level and would not be suitable for this type of setup. (because then you would be controlling volume on the monitors and subwoofer themselves, which means having to adjust two volume controls each time you make a change)
If your TV doesn't allow for this, you would need to get a preamplifier to control the volume, or buy an integrated stereo amplifier (with a passthrough) and get bookshelf speakers rather than active monitors.
Alternatively, there are some 2.1 "desktop" or "multimedia" (PC) speaker kits that have a powered subwoofer, which has an amplifier that drives both the sub and the stereo speakers. The Corsair SP2500
would be an example of that. I'm quite sure that companies like Logitech have similar offerings - but I can't speak to the quality of any of those.