If the TV has good sound and if the analog audio outputs on the back of the TV are controlled with the TV's volume control, you can just add a sub to the TV and it should sound spectacular. It won't be surround, but it will give you the excitment that only a sub can do. Besides, there are two reasons for doing it this way...

First, It could give you more money for a better TV and second, if you decide that you prefer a surround system, you haven't lost any money cause you already would have the sub.

HSU and SVS makes good subs for the money.