In your example you don't use the 's': When you say '2 million cars' for example , 'million' here acts as a determiner describing the successive noun by quantifying it and you know that determiners as well as adjectives stay neutral regardless from the noun they precede,whether it is in the singular or plural form. However when you say : " Milllions of cars are produced annuallly in this factory." Here 'million' is a noun and it has to portray the singularity or plurality of the subject ( here:car).

We do not put 's' after numbers such as hundred, thousand, million etc when we talk about a specific quantity . So no 's' in '..below 2 million to over 30 million.' We use 's' when we talk about unspecific quantities. 'There are millions of car owners in the world.' 'The number of car owners has grown by millions.'

This will all depend on when and how you use the numbers.In your sentence they are correct without the 's' Cherrys answer is perfect, let me just give you another sample sentence to help a bit more. Thousands of protesters lined the streets, police estimate their numbers reached at least eight thousand or more.

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You can say:Hundreds/thousands/millions of dollars were spent by the government