This is a simple WordPress shortcode to add a Paypal button

paypal-shortcode.php

<?php
/* 
Plugin Name: PayPal Shortcode by Darren
Plugin URI: https://gist.github.com/3266387
Description: This is a simple shortcode to add a Paypal button, just use [paypal] as the shortcode.
Version: 0.1
Author: 
Author URI: 
License: 
License URI: 
*/

function dm_paypal_function () {
	$productid = get_the_title();
	$price = get_post_custom_values('item_price');
	echo print_wp_cart_button_for_product("$productid", "$price[0]");
}

add_shortcode('paypal', 'dm_paypal_function');

Thanks for the help :)