00-add-custom-user-input-woocommerce-product.php

<?php
add_action( 'woocommerce_before_add_to_cart_button', 'add_ad_budget_input_field' );
/**
 * Output the text input field for #sem_ad_budget - hooked to woocommerce_before_add_to_cart_button().
 *
 * @return void
 */
public function add_ad_budget_input_field() {
	// Bail if not SEM product ID.
	if ( !is_single(1234) )
		return;

	// div for jquery slider.
	echo '<div id="sem-slider-range"></div>';

	// args for woocommerce_form_field()
	$args = array(
		'type'        => 'text',
		'placeholder' => 300,
		'label'       => __( 'Monthly Ad Budget', 'text-domain' ),
		'description' => __( 'Enter a maximum budget for each month.', 'text-domain' ),
	);
	woocommerce_form_field( 'sem-ad-budget', $args );
}

add_action( 'woocommerce_after_add_to_cart_button', 'add_ad_budget_custom_message' );
/**
 * Echo a message to display if ad budget is over $XXX
 */
public function add_ad_budget_custom_message() {
	// Bail if not SEM product ID.
	if ( !is_single(1234) )
		return;

	// Output message if budget is over $XXX
	echo '<div id="sem-product-custom-budget" style="display: none;">Please contact us for a custom quote.</div>';
}

add_action( 'wp_enqueue_scripts', array( __CLASS__, 'enqueue_ad_budget_scripts' ) );
/**
 * Enqueue scripts needed for adding custom input field and
 * auto selecting product variation based on input.
 *
 * @return void
 */
public function enqueue_ad_budget_scripts() {
	// Bail if not SEM product ID.
	if ( !is_single(1234) )
		return;

	wp_enqueue_script( 'jquery-ui-slider' );
	wp_enqueue_script( 'sem-budget', MY_PLUGIN_URL . 'assets/js/sem-budget.js', array( 'jquery-ui-slider' ) );
	wp_enqueue_script( 'jquery-ui-slider-pips', MY_PLUGIN_URL . 'assets/js/jquery-ui-slider-pips.js', array( 'jquery-ui-slider' ) );
}