the company I work for bills me ( a junior designer) for 95 bucks an hour to clients (most of whom are fairly well off)
and we often spend a great many hours develloping logos.
I also do work on the side, and often do things just for the hell of it for a whole lot cheaper...it depends on what you want out of it.
I would say NO LESS than 250 dollars for a stand alone logo, and if additional work is required (cmyk, pms, rgb, vertical, etc etc) then charge them for the time obviously.
but if you're just starting out, and you think a company will use your logo it maybe we worth it to let them have it for cheap just to have something in production...which is invaluable.
there's more than just monitory gain with something of this nature.