Your CPU won't handle BluRay without a new video card. I recommend one of the cheaper HD4xxx cards.
You also need a program that supports and plays BluRay movies (like Cyberlink PowerDVD). I doubt you can find one for less than $50.
So you need three things in total and that's going to run you over $200.
If you are trying to build a Home Theater for your HDTV I don't recommend it. Get a standalone player. In fact, I recommend waiting for BluRay computer players to come down in price if you need one. I'm waiting until a BluRay burner with good reviews is less than $75.