My post office gal Jennifer tells me there will be a break on price if you use Click and Ship, but it's hard to tell how much:
"Express Mail is switching to a zone-based pricing system, resulting in customers paying less for nearby destinations. Customers will receive a 3 percent price reduction by purchasing Express Mail online or through corporate accounts. Additional price reductions are available for those who ship quarterly minimums.
Priority Mail will have an average 3.5 percent savings for customers who use electronic postage or meet other requirements. "
Hollis