Right now prepaid cards are mainly used for the following use cases.
1) for a number parking, receiving SMS OTP or app registration
2) occasional data use case
3) used by foreign workers who may have some constraints to buy Postpaid plans
4) used by tourists
But technically you can also use the prepaid cards for regular data usage, not too bad if compared with other 5G plans (not considering special offers like eight/SIMBA one to one top-up offer and Singtel MVNOs' three months or six months 50% OFF offer).
1) Singtel Prepaid 5G at S$15 per 28 days
https://www.singtel.com/personal/products-services/mobile/prepaid-plans/hi-sim-cards
SingTel hi! S$15 SIM
hi!Surprise S$15 top-up offer (only from Singtel hi! Prepaid app)
500GB 5G+ data for 28 days
250GB Singapore + 250GB Roaming
(Malaysia, Bangladesh, India, Indonesia, Thailand)
500 Local Mins & 100 Local SMS
Up to 600 IDD Mins
2) M1 Prepaid 5G at S$14 per 28 days
https://www.m1.com.sg/mobile/prepaid-plans/m-card/sim
https://www.m1.com.sg/mobile/prepaid-plans/m-card/top-up
M1 S$14 prepaid SIM card
M1 S$14 all-in-one top-up
500GB all-in-one 5G data for 28 days (Singapore, Malaysia, Indonesia, Hong Kong, Macau, Taiwan)
3GB roaming data (Bangladesh, India, Indonesia, Thailand)
500 Local Mins & 50 Local SMS
200 IDD 033 Mins (Bangladesh, China, India, Indonesia, Malaysia, Thailand)