District Judge Kessler Soh said in handing down the sentences that "terrorism is a clear and present danger" which presents a "threat not just to our community but the international community at large".
Ringleader Rahman Mizanur, 31, was jailed for five years, the longest of the sentences. Two others, said to be the treasurers of the group, were each jailed for two-and-a-half years and the fourth man got two years.
"Terrorism financing and any act of supporting terrorism must be roundly condemned and deterred," the judge said.
"Stiff punishment is needed in this case, not just to punish but also to deter others."
The four, the first suspects to be prosecuted in Singapore under a new anti-terror law, were brought to court under heavy security by members of the city's elite Gurkha unit.
Dressed in purple jumpsuits with the words "detainee" emblazoned across their backs, the men were shackled hand and foot.
Court documents said the men contributed, collected or possessed funds for the alleged plot ranging from Sg$60 ($44) to Sg$1,360.
Items seized from the men included manuals on bomb-making and how to use a 0.50 calibre sniper rifle, along with a list of Bangladesh government and military officials targeted for attack, Singapore's home affairs ministry had said.
They were among a second group of Bangladeshis rounded up in Singapore since 27 were arrested in late 2015, also over alleged plots in their homeland. All from the first group have since been deported.
Singapore, which depends heavily on Bangladeshis and other foreign workers in the construction sector, considers itself a potential target of extremists because of its strong military ties with the United States.