From now until 31 Mar 2021, spend a minimum of S$500 using your American Express card and you’ll have the opportunity to purchase KrisFlyer miles at 1.48 cents each.
Here are the Amex cards eligible for this promotion, which includes the Amex Platinum Charge Card and Amex KrisFlyer cobranded cards:

Note that you will need to enrol yourself for this promotion as per the instructions below:

Upon meeting the minimum spend requirement, you will have until 15 Jun 2021 to make payment of the one time fee, before receiving the miles in your KrisFlyer account by 31 Jul 2021.
Depending on how you value your miles, this price point is decent enough should you need some additional miles to plan for any upcoming trips once mass international travel resumes.