I buy it from some buddies per hanging weight yearly, however, keep in mind, the hanging weight is NOT what you will actually get AFTER it's processed. You can figure if you're getting half a cow and they tell you then hanging weight is 250lbs, you can expect the actual weight being bought after being processes around 188lbs (you can figure at least a 25% reduction in processed weight).
Generally I tell the butcher what kind of cuts I want from the cow. Hamburger, stew beef, sirloin, T Bone, rib eye, chuck roast and filet / steak.
I can generally keep 300lbs of meat in my freezer with some spare items already kept in there.
Below is a whole cow, belive this one came in about 550lbs hanging weight.
I will say this... trying to find someone to buy a portion of a cow is a PITA.
When I tell a man I'm going to do something, I do it. Finding a couple of people to take a couple of cows you can figure people are going to back out on you which adds to the PITA factor. One reason why I'd like to think people will ask me if "I'm in" for a cow. When I tell them yes, they know I'm good for it.
The issue is IMO the best bang for the buck after processed is to buy a variety of cuts and not just hamburger unless you find another buy of a portion of a cow who would prefer more steak cuts. The reality is the butcher can only do so many steak cuts from a cow, and people just starting in tend to want to buy always want the best cuts.
From experience, I'll say this... whatever you buy per a portion of a cow, weigh everything before you put it in the freezer. Sometimes people make mistakes. Took a while for me to figure that one out.