You haven't factored in the cost of replacement backing pads and interface pads yet.
For most of my work with the ETS 150, I prefer using the blue hard backing pad over the soft pad that comes with the sander.
Just a side note, I checked the price of a new backing pad and it's being advertised at $71.20 but this includes a 20% limited time discount, this can't be right can it,
as the last one I bought I'm sure was $50 something last year, that makes the new price when the discount ends to be about $85, for a backing pad?