In addition to being able to borrow MR points from Amex, you can purchase them outright, up to 500,000 MR points per year. The cost is $0.025 each. It would make sense to maximize your MR borrowing capacity as described above first, as the worst case is that in one year you'll have to buy miles at the same price to repay the points loan should your spending not cover it. But can often be the case that a MR points purchase makes sense, if you're just below the threshold of having enough miles to redeem for an award you really want.