How to explain punctuation in these 3 cases?

The first sentence is understood as

Many users mentioned that the budget friendly price makes this software attractive for beginners, and [many users mentioned] that you get a lot for your money since it features 25 built-in lettering fonts and five monogramming fonts.

“that the budget friendly price makes this software attractive for beginners” is a noun clause (a content clause) and is the object of “mentioned”

“that you get a lot for your money since it features 25 built-in lettering fonts and five monogramming fonts” is also a noun clause (a content clause) and is also the object of “mentioned”

You can reduce the whole sentence to “Many users mentioned A and B.”

You will note that there is no comma following “A”, however there is one following “beginners”. That comma is not required but it is inserted as a “pause” comma to aid reading because the first object clause is quite long.

The dash between “software” and “a simple” could be replaced by a full stop, a colon or a semicolon – it is conjunctive but a comma would be wrong as it would result in a comma splice.