I receive MR points on cheapie Hertz rentals, and while they *do* post fairly reliably, you can't count on them to show up that fast.

Assuming you are a "normal" Marriott guest - that is, you've earned your points by staying in the hotels and have an active account - I would guess that odds are very high that they'd "loan" you the points.

Worst case, the $10 for 1,000 points is a good way to go. Usually buying points or miles from any provider is at a very punitive rate, but honestly $10 for 1,000 is quite fair.