Even the 553ELX which uses standard batteries without an adapter costs less than a 500C/M. The extra bulk and weight of the motorized cameras make them less fun to use outside and handheld. They are more at home on a tripod in the confines of a studio.
I find the motorized bodies are easily handheld by wedging my right thumb between the magazine and motordrive while my middle finger rests on the release. Left hand takes care of the focusing and f-stop/shutter work.