In short, before specifically pointing out that the merchandise in one place is more expensive than in another place, you would probably have to: 1. know that that matters to this person. 2. point out all the maalos of the more expensive place (and that would be assur in a public place since you are putting down the other place and it may not be l’toeles for everyone reading it).
Bottom Line: There are many factors and conditions. Ask a sheilah.