Your rotors and pads develop the same wear patterns over time. Replacing one without replacing the other is like replacing the Yin without the Yang... you'll just end up copying the wear patterns onto the new/flat parts.
One option is to sand the pads down smooth and flush, similar to the rotors. But quite frankly, having just done mine this past weekend, it'll cost you about $120 for new front rotors and pads if you install them yourself. And fyi, have an impact wrench and a breaker bar handy to get the rotor retaining bolt and the pad carrier nuts off. Oh, and my rotors were practically rusted onto the hubs, so have some liquid wrench handy and bang away at the back of the old rotor if need be with a hammer.