They will be priced the same at any t-mobile store (plus whatever the local sales tax is).

However, if you go into an authorized dealer, which may look like an official t-mobile store, they may mark them up.

Not that you asked, but keep in mind t-mobile filters some content on their day passes, per their FAQ's

Web Guard is automatically active on Web Day Pass purchases and cannot be disabled. Some Web sites may be blocked due to the nature of the site, including but not limited to:

Abortion, Alcohol, Ammunition, Criminal Skills, Cults, Drugs, Firearms Accessories, Gambling, Guns, Hacking, Hate, Knives, Lifestyle, Martial Arts, Mature Content, Occult, Pornography, Suicide, Tobacco, Violence, Weapons.
Partially-restricted content includes the categories of Personals/Dating and Sex Education.

If that matters