How to override price-utils.js specific method?

Using mixins is to follow the best practice. But in your script, should try:

define([
    'jquery',
    'underscore'
   ],
    function ($, _) {
        'use strict';
        return function (target) {

            target.formatPrice = function formatPrice(amount, format, isShowSign) {
                //Your custom format price here
            };

            return target;
    };
});

[EDIT] Add others dependencies if we want.