Using space instead of comma for large numbers?

Is there a package I could use to insert a space instead of a comma for large numbers?

For example,

12 345.67

instead of

12,345.67

If needed, I am using the extbook environment. All of my numbers are in math mode.

Edit: Is there a way I can do this formatting without having to type in num (from siunitx) for every single number?

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