If only it were that simple. Every shopping cart (Zulu, Magento, AspDotNetStorefront), hosted service, and marketplace (eBay, Amazon, Bonanza) has different capabilities, which affects the schema of the product catalog.
Compare your existing site with your proposed cart/hosted service. Do they have any of these features?:
Kits, Quantity Discounts, Ship-separately items, Variations (size, color, style), Restricted Quantities,
Upsell items, Tag-along items, Shipping Dimensions, Shipping Restrictions (HazMat), Gift Wrapping Option, Free shipping.
Then there are search-related attributes, which are tied to the specific cart/hosted service search facility:
Genre, Year, Manufacturers Part Number, Manufacturer, Publisher, Ships Free, Horsepower, Hand (Left/Right), etc.
Can Product Variations vary by weight and/or price? Can Product Prices vary by Currency? Can shipping rates be specified for each item? Are quantities stored as integers, or do they include decimal places? Can products be placed in multiple categories, or just one? How are your URLs (as indexed by Google) going to be carried over and redirected?
As a simple test, try mapping products from eBay to Amazon (two well-known marketplaces). The common attributes are easy, and can be done in an hour. But Variations are completely different, shipping methodologies don't even compare, product feature bullets (for Amazon search) don't have an eBay counterpart, and the pricing model is different (one uses US-only tiered rates, while the other gets International real-time rates from carriers). The two biggest marketplaces on Earth, and you'd think that moving from one to the other would be a snap.
Don't believe that a programmer can do this for a couple-hundred dollars. It's been my experience that taking 10,000 products from one cart/service to another is *not* a weekend job. The common information (Name, Description, Price) can be done in a few minutes. The difficulty is dealing with the things that don't map over.
The task of picking-up and plopping-down, with no disruption in operation, is measured in man-weeks, not minutes.