Moving UB Teachings from Pauper to "casual", good budget cards to add?

So my coworker was getting his ass kicked by his buddies at the kitchen table, so I lent him UB Teachings to get even. Well I have created a monster, he LOVES the deck. I decided to let him keep it if he buys me lunch.

Being that he isn't restricted by a format, I was thinking about good cards to add to the deck. Unfortunately, I am a spikey dude so I kept on thinking of expensive Modern and Legacy staples. What are some powerful cards to add to the deck that are inexpensive, now that it isn't restricted to only commons?