直接去，立马搞定，几十块吧。
请参考下文，你的问题答案我加粗了：
For legalisation of documents at Ministry of Foreign Affairs (MFA) Singapore , no prior appointment is required. You can bring the
documents directly to the Consular Service Counter at MFA building and the legalisation procedures can be completed on-the-spot.
Contact Details:
Ministry of Foreign Affairs
Address & Office Hours: Consular Service Counter
Ministry of Foreign Affairs
Tanglin Singapore 248163
Mondays to Fridays 9.00am to 12.30pm and 2.30pm to 4.30pm
Saturdays: 9.00am to 12.30pm
Tel: 63798000
Cost per document: SGD$10
Payable by Cash, Nets, Cheque or Cashcard.
祝早生贵子！