You don't want to skimp on the power supply, especially if you add a higher end video card (a waste for MAME, but great for PC games).
Antec is a good bet but you pay for the brand.
Forton and Sparkle are two good brands that tend to be much cheaper (but hard to find locally so you needs to order on the 'net). The very minimum you want is 350W, I'd go with at least 400W. Google for power supply buying advice, what's important is not the "total watts" but the +12V and +5V total output.