198,000 など、3桁ごとにカンマを入れるのがめんどくさかったので、ごくごく簡単に作ってみました。

set thePrice to 198000 as string

set AppleScript's text item delimiters to ""

set thePrice to every character of thePrice

repeat with i from (count of thePrice) - 3 to 1 by -3
    set item i of thePrice to (item i of thePrice & ",") as string
end repeat

display dialog (thePrice as string)

ハンドラで使用する場合は

display dialog (makeComma(198000 as string))

on makeComma(thePrice)

    set AppleScript's text item delimiters to ""

    set thePrice to every character of thePrice

    repeat with i from (count of thePrice) - 3 to 1 by -3
        set item i of thePrice to (item i of thePrice & ",") as string
    end repeat

    return thePrice as string

end makeComma

現状では整数のみで小数点には対応していませんが、ひとまず。