Hi, I am thinking of doing monthly DCA (~S$2k) into Ireland-domiciled funds (e.g. CSPX) that are listed on London Stock Exchange. Can TD Ameritrade do that, and is it the cheapest?

They only trade U.S. domiciled equity.

Standard Chartered could do that job for You, I feel they are reliable, and reasonably cheap, even when not the cheapest. Also: the fees will drop anyway step by step in the future. With 2000 SGD lump sum investments the relative fees for you will be tolerable.

Make sure that the currency conversion of your outgoing SGD for these transactions is not done by your banks or brokers, but by a cheap & reliable service like, f.ex. TransferWise. The bank / broker own conversions are mostly intransparent and expensive.​​​

No, TD Ameritrade only allows you to access the US stock exchanges.

You have to look at other options.