Well it's just about the same rate. right now the stamps cost me .48 and a half cents for one first class stamp. Where at the Post Office it cost .49 each. The price is almost the same but tracking comes free for first class packages. That along saves like a buck on each one. I did bid on a couple of your auctions so hopefully I can win and you can combine shipping for me. Stamps.com does save on packaging materials and gas & time too. If you ever get interested let me know and I could point you in the right direction and you get a free postal scale and some postage to start you off with free postage too. There is a monthly charge for using the service though of $14.99 but I think it's worth it for me.
I love it, they even come to my house to pick up my outgoing stuff. Very handy especially when doing selling online and auctions too. Have a good night :)