I'm assuming you mean a stereo amp for a pair of Energys.
You may want to try something geared for optimal two channel performance that delivers more current per channel, as opposed to watts.
You can pick up a used Musical fidelity A3CR like the one I use or several other similar MF amps in the $500 range or slightly more. I suspect an A3CR would bring the most out of your Energys.
You can definitely do better for less going used for amps but for obvious reasons, you must be careful and make sure you know exactly what your getting in terms of condition and age of the unit and its ownership history, if possible.