Car Audio Amplifier Testing... What equipment?

I need to know what equipment i need to test efficiency of an amplifier, I know i need dummy loads, a power invertor and oscilliscope. Where is a good place to get the resistors and what are some well regulated power supplies that have selectable voltage (12.5, 13.8, 14.4, etc.), I was looking at VELLEMAN HPS10 for an oscilliscope, seems pretty straightforward to use and I really don't feel like dropping thousands on the equipment. Thanks all! -Kenson