You can either incorporate the shipping into the price and say something like "$90 shipped" for the leopold, or "$75 + shipping", in which case the shipping will be calculated based on location. Shipping cost is estimated on USPS, Fedex, or UPS website based on weight and location.
Just to help you out a little bit, a TKL weighs 35 ounces, the retail box and accessories weighs 12 ounces, and your packaging should weigh roughly 11 ounces. But since you have a full size keyboard, it's just a tad more. Last time I shipped a full size Filco, It was over 3.5lbs, but under 4.0lbs.