SafePrice when it was integrated was a part the Avast Online Security - Browser Protection in the avast Tools section of the avast custom install and can be uninstalled as outlined by Eddy.
You can also change the settings in the Avast Online Security (AOS) browser add-on and uncheck the SafePrice option.
That said the SafePrice was dropped from installs from later avast program updates/installs and was a stand alone installation. However, if you had previously had it as part of the AOS add-on then I believe it would still be present on program updates unless you did a custom install.
The article that you reference is from April 27, 2014 and things have changed considerably from then.
The advice to "Register with a dummy email address to avoid getting more Spam" could well cause you more problems and installations of avast have to be linked to your my.avast.com account and that requires validation of the email.
Having used avast for almost 11 years I have no idea what spam they are referring.