If your TV in question will be used as the main Television than a min. of 5.1 surround sound will be sufficient. To work within your $300 budget is not impossible. Many companies sell a complete system for cheap that comes with a blu-ray player.
A sound bar will not give you the theater experience by giving you the feeling of being in the movie.
Sound bars should be used on televisions used as a secondary TV such as in the bedroom, kids room, bathroom even the kitchen. They give you better sound than the built in speakers period, but for the money a basic inexpensive 5.1 surround sound system will give you a better feel.