WP Premium Shopping Cart Plugin

Creating a new site using WP. Need a professional/premium shopping cart to plugin to the site.

Cart must have the following: UK compatible (for VAT purposes), Google products/base CSV export, variety of payment gateways inc PayPal and Google Checkout, stock control (ie shows stock levels on buy page), quantity discounts, postage calculator (preferably with Royal Mail), coupon feature (for promotions), SEO optimised etc ….

Have a reasonal budget up to about ￡150

Any ideas, please let me know