What is an appropriate cash amount to start investing in stocks or EFT/REIT (without using RSP or robo-advisors)?

A good start would be 2k. But it depends on your own financial health! Don't invest money you need in the next 1-2 years into the stock market. Hope it helps👌🏻

(500, 1000), better 2000 SGD would be a good start to have relative commission fees down.

The lower the broker's fees, the lower could be Your investing amount to buy cheap.