hey man, good on you for thinking ahead! i think the most practical option is to find a local supplier since shipping bulk salt is a huge cost.. i see you're from Colorado so there must be a supplier in your area that specializes in snow and ice control products.. your timing is even perfect since there might be suppliers already offering pre-season pricing so that can save you a good chunk of change!
as for how much to get, a good rule of thumbs is around 750 lbs per acre of surface you need to cover, but you have to factor in how much of an average winter you get.. the colder it gets, the more salt you'll need. i suggest you make sure to pre-treat before a storm so you'll use less than if you're trying to melt a thick of ice after the fact. it's always smart to get a little more than you think you need. salt stores well anyway, and you don't want to get caught short in the middle of a bad storm!
