Best buy for the $$ is going to depend largely on the caliber that you want to use. To me, that is the starting point of any discussion on handguns. Once you settle on that, I think you will be able to get some solid advice from the board.
For my part, I believe that the best value on the market today is the CZ75B in 9mm. Proven cartridge, outstanding design and manufacturing by the company, and they can be had for under $400.
But, like I said, you'll need to come up with a "caliber of choice" first. And if home defense is the primary objectice, then I concur with the pump shotgun advice. The sound of a racking slide is generally followed very closely by the sound of racing footsteps, headed in the OTHER direction!