Marriott Rewards allows members to purchase up to 50,000 points for $625 every calendar year. That is 1.25 cents per point.
Starwood Preferred Guest (SPG) sells maximum of 30,000 Starpoints every calendar year for 3.5 cents each before any campaigns that they have every few months.
SPG usually sells Starpoints during campaigns at 30% off and had one campaign this year when they were selling points up to 35%. That is the highest discount I have seen and made a purchase at the time and paid $682.50 for 30,000 points (2.28 cents each). You can read the price that I wrote about my purchase here.
I purchased 50,000 Marriott Rewards points back in March and paid $625.
If you purchase the 30,000 Starpoints when there are no sales and convert them to Marriott Rewards points at 1:3, you end up paying 1.17 cents each which is less than what Marriott charges. If you can catch a sale as good as I did back in May, the price of a Marriott Rewards point can be as low as 0.76 cents each.
Note that there is no guarantee that SPG will continue selling points at a discount now that Marriott has taken over or that they would not raise the price.
Obviously there are no guarantees that SPG and Marriott will continue selling points at these prices.
They are, however, a good deal still if you are redeeming for travel packages and combined with bonuses that American Airlines and United usually offer once/twice a year for hotel points to airline miles conversions.