All Starwood Preferred Guest (SPG) members now have the opportunity (probably the last one before the merger of the SPG and Marriott Rewards program happen) to purchase Starpoints at 35% off from now until 31 May 2018. Do remember that you are only allowed to purchase up to 30,000 Starpoints per calendar year and in the event that you do not use them before August 2018, these will be converted into Marriott Rewards points at the end of the period.
For every 20,000 Starpoints at you convert into airline miles, you will get a 25% bonus - this means to say that if you were to convert 20,000 Starpoints into Alaska Airlines MIleage Plan miles, you will get 25,000 miles which is sufficient for two Business Class intra-Asia flights on Japan Airlines (you may check out my review of JAL's SKY SUITE III product HERE!). On a regular day with no promotion, you can purchase 25,000 Alaska Airlines MIleage Plan miles for approximately USD 739 (inclusive of tax recovery fee). If you do manage to take advantage of the 40% bonus on Alaska Airlines MIleage Plan miles, the cost of acquiring 25,000 miles is approximately USD 528.
In comparison, purchasing 20,000 Starpoints at 35% off now (which converts into 25,000 Alaska Airlines MIleage Plan miles) will only cost you USD 455 which is significantly cheaper. Regardless of what you actually intend to do with these Starpoints, purchasing them now at 35% off is a great idea and I highly recommend checking out the award charts on partner airlines to see if you can find a sweet spot for an amazing redemption.