In English the verb To be is used in both cases but in Spanish those are two completely different verbs with different meanings. The full explanation could be a long one but the short one using your example is like this.
"este está más barato" means that at this moment one article is cheaper that other in a temporary situation likely to change shortly, however you could also say "este es más barato" meaning that one article is in generally/usually/always cheaper than the other.
The other example is similar and it states that the current state of one of the objects is being newer (less used) that the other, but that is also a situation that could change in time.
It is not the same to say "Esa mujer es muy bonita" oposite to "Esa mujer está muy bonita". I hope you now can think of situations where this last example applies.
ser is usually used to express a permanent state/property of something while estar is more of a temporary thing, but as I said these two are possibly the more complex verbs to learn.
BTW if you use the search tool on this site for "ser estar" you will get more than a hundred questions that will help you learn more about these two verbs.