I'm assuming the Walmart website reflects your local pricing in the US.
Walmart link to the HP DeskJet 3420 Color Printer
Looks a wee bit more expensive at $78.42... including cartriges.
Also note that it says Online only. Okay... if some of your local stores are selling these they are likely doing it in their specific locations only, meaning they are in all likelihood store only specials and not going to stay that price very long. As I see it right now, someone is mistaken about the price.
Now let's move on to the cartriges...
#27
#28
for a total for the two together of $49.18.
Have I missed anything?