I usually plan on quarters at 70 lbs each unboned, and that I'll be under that if I bone it out. There are occasions where I prefer packing it out bone-in. But, I don't think it's unreasonable to expect somewhere between 150 and 225 pounds of venison. My last elk fit nicely in a 14 cubic foot freezer with room enough for a few pheasants.

Freezers are the easy part though. Whether you take your elk to a processor or butcher it yourself, you should have plenty of time to go out and grab a freezer and get it cooled down. Or maybe I'm just a slow butcher?