+1 for a 2" X 72" grinder. Since it's the most common, belts are easier to come by, and will be available in a much wider array of grits and quality than either of the sizes you mentioned.
It's a balancing act ....trying to get the most machine for your money, but do yourself a favor. Save the money and by a "good" machine. By that I mean be prepared to pay $1,000-$2,000. I know that's a lot of money, but trust me, you will be disappointed in anything less if your going to make blades.