Right now, you can get the Vizio SB2920-C6 on Amazon for a low price of $65.99, which is about as cheap as the soundbar has ever been. It's a 29-inch, 2.0 channel soundbar suitable for TVs in a wide range of sizes.
It's a simple and easy-on-the-eyes item with Bluetooth connectivity, but note that you won't get a subwoofer or the newer SmartCast system from 2016 here. This particular Vizio SB2920 model is sold directly by Amazon, too, which adds some welcome reliability.
You could also spring for the SB3851, and 2016 model that's $100 off its usual price right now. If it seems pricy at $200, that's only because you haven't heard what's in the box: a buncha stuff.
With the SB3851, you get a fully SmartCast compatible speaker system, including a big 38-inch, 5.1 channel soundbar; two wired, rear tweeter speakers; and a wireless subwoofer. The whole thing creates a pretty formidable little surround sound system, and getting it for $200 is definitely a bit of a steal.
Just be aware that this deal is primarily from third-party sellers, and check buyer feedback judiciously.