That's a hard one because of the price. But let's take a whack at this. Your first task is to find out 1) if their TV has a headphone jack, 2) is the jack stereo, and 3) if the remote controls the volume of the headphone jack. If so you may be able to get away with a set of computer speakers like
Klipsch's Promedia 2.1. They won't fill a huge room but they will do fine at moderate volumes in a smallish room.
Or you could do a pair of
Behringer 2031Ps ($160 shipped) and a refurbished
Onkyo TX-SR 307 receiver for $159 plus S&H. The 2031P isn't supposed to be as linear as the 2030P but if you aren't going to add a sub it's a better choice.
About the only other thing you're going to in that price range is some kind of all in one sound bar/box like Bored suggested.