Find Array of Rang of substring in NSMutableAttributedString

Question

I have a attributed string with $ sign like this " price 1 $ 25 \n price 2 $\n price 3 $" I want find all the ranges of "$"

let attrString = NSMutableAttributedString(string: " price 1 $ 25 \n price 2 $\n price 3 $")
let ranges = // all ranges for $ sign

I need to set different color for "$".

I know how to find range in attributed string.

extension NSAttributedString {
func rangeOf(string: String) -> Range<String.Index>? {
    return self.string.range(of: string)
}}

I am wondering how I can find an array of ranges of "$" sign in a given attributed string?