Under $100: A Good 4-button style charger with at least 10W discharge and 80W charge. Gens Ace Imars III Pro, "B6 v2" chargers.
$100-150: Gens Ace IMars D300 (300W AC/700W DC). Up to 15W/3A discharge per channel, 300W AC charge power to split between the channels (enough for 2 6S 6000mAh batteries at 1C)
$150+: Junsi iCharger 308DUO/456DUO/458DUO/4010DUO- tons of power with a proper power supply, the racer's choice.