Understand that I am relatively new to MTG, so take my advice with a grain of salt. After looking at your deck, if I understand your deck's objective correctly you want to create scions really quickly and sack them to build up creatures like
Nantuko Husk, and
Rot Shambler. The pairing with
Zulaport Cutthroat is excellent, and along with
Bone Splinters and
Evolutionary Leap you have made good choices.
However, instead of
Sultai Emissary and
Qarsi High Priest you might want to go with
Carrier Thrall and/or
Call the Scions. The downside is that your average casting cost is higher, but the upside is that these cards are more in line with the objective of your deck (generate scions; sack them while hurting your opponent, gaining life and using the scions for removal; and build up
Nantuko Husk or
Rot Shambler for the final attack). Since games in Standard format tend to go longer this may be a viable change.
Carrier Thrall is 30 cents per card, and
Call the Scions is 19 cents per card. This should be in budget.