I have this for about 2 years and it was free then. I don't think this cost money at all.
Interestingly, I logged into the USPS website with a login and password that I have had for several years. I clicked MyUSPS, and they told me:
"As a business user you are not eligible to participate in the My USPS program. If you want to participate, please create a new USPS account and register as a personal user."
I must have signed up for a business account. I guess I can now sign up for a personal account.