Replying to Prices just went up on shirts and other things?

I was just browsing the store earlier today and i bought a Dino tee(woot woot) and a sticker pack..The dino tee was 16$ and the sticker pack 5..After 5min ago I just checked back and the price of the dino tee is now 20$ and the anti gaper is 19(up from 15)..so I was just wondering why the sudden increase? and will I have the pay the difference since I literely(sp) just bought something right before the change?

Thanks!