I'm on the west coast (CA) and offer free shipping for my Ebay listings. My suggestion for coast to coast shipping would be to find the max shipping cost and factor that cost into the total price. For example, I can use my CA zip code and enter 10007 as a destination zip code on USPS.com to get the cost. Say it's $12 for a 2lb Priority package. That $12 gets factored into the Free Shipping price in the listing. If you want to get more exact, do a reverse search for a legit address (Zillow, Google earth, etc) for John Doe at Paypal/shipnow for an exact shipping cost.
Likely, the average across the country it pretty even for the states west vs east. If a Death Star ships 1 state away, there's more cash in my pocket. But if it goes to Maine, I know I'm covered. Remember, the buyer pays the shipping, not the seller if you offer free shipping and do it right. Set it up when you list the set and you won't have to worry about it when it sells.