@Manish MittalNo, not working, anythis else i forget to add, pls check.
di.xml => https://snipboard.io/VOs0Ny.jpg

PriceBox.php => https://snipboard.io/InsWo7.jpg

Please follow basic Magento standards to create a module. where modul.xml and registeration.php file for this module?
app/code/MM/Training/registration.php
<?php
\Magento\Framework\Component\ComponentRegistrar::register(
\Magento\Framework\Component\ComponentRegistrar::MODULE,
'MM_Training',
__DIR__
);
app/code/MM/Training/etc/module.xml
<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../../../../../lib/internal/Magento/Framework/Module/etc/module.xsd">
<module name="MM_Training" schema_version="0.0.1" setup_version="0.0.1"></module>
</config>
Run php bin/magento setup:upgrade to enable this module
I have created this module first MM_Training.