I have notice that the prices of MtG Cards are different in my main inv than compared to my deck listing. For instance, my inventory still list Ulamog around 30-32 in my inv, but in a deck listing that the card is in, it is at 23. Not sure if this is a bug or something I have done.

Please disregard, I am a doofus and didn't realize the Ulamog I have is from Rise of the Eldrazi, not MM15, which is the listing price of the Ulamog in the deck.

Yup, decks currently show the price of the most recent major printing of the card.