If I were you I would mainboard: taigams scheming, Liliana, heretical healer, and evolutionary leap. If you go the aristocrats route, I would also run hangarback walker, hooded hydra (personal opinion), and zulaport cutthroat.

Eiyros I wish I could run Taigam's Scheming and Evolutionary Leap, but my deck is clogged with two drops as it is. I had Taigam's Scheming in the earlier versions of the deck, but I had to cut it. You'll see the Leap in the sideboard against removal-heavy decks. As for Liliana, Heretical Healer  ^Flip, I'm trying to keep this budget for the moment, but if I can afford her, I will definitely put her in.

Cool beans. Honestly though, evolutionary leap is worth running like two copies in the main board. I would remove corpesweft if I were you for it because it exiles creatures from your graveyard, and in your deck most of your creatures reanimate themselves from the graveyard. If you want something that loves delve and hits hard, run torrent elemental.

i forgot to mention if you choose to spend more on this deck, run the den protector/ death mist raptor combo

Eiyros Making some changes to the deck. I think Leap will make its way in. Torrent Elemental is something I will also consider.

nateblego, ninjaclevs13, Eiyros and TMBRLZ I made some changes to the deck; read the newest update for a full description. What do you guys think? Is there anything else I can change, keeping budget in mind?

The deck and description looks sweet, I'm still a firm believer in Monastery Siege though. What cards are you using to represent Kalitas and Stoneforge Masterwork? They aren't in the TappedOut Database yet. Gather the Pack was a good call. Have you considered Murderous Cut? With all the delve fuel, it would be a really strong removal option, and I think this deck needs some removal. another removal option is Reality Shift, because downgrading a Siege Rhino into a 2/2 that you can kill with a Screeching Skaab is pretty sweet, and it's always really funny to manifest their Ugin, the Spirit Dragon.

I feel like Corpseweft isn't quite worth it, several of your creatures have graveyard recursion and Graveblade Marauder wants to have creatures in your graveyard. I would consider cutting it for Murderous Cut or Reality Shift.

This deck is starting to look really tight, I hope it does good! +1 from me.

A few other thoughts:

Sultai Emissary synergies really well with Nantuko Husk, but not with the rest of the deck. I feel like Nantuko Husk should be primarely used in this deck to repeatedly grow huge by abusing Risen Executioner and Bloodsoaked Champion. Maybe consider cutting it for removal or Taigam's Scheming?

The other thing is Torrent Elemental. It isn't a zombie, but it's amazing with the rest of the deck: you can dump it in your graveyard, delve it, and then bring it back. Once it's on the battlefield, the real fun begins. A 3/5 flyer is strong stats, but it pushes through a ton of damage by basically making all of your guys unblockable. I strongly advise that you put him in the deck, possibly replacing Sultai Emissary as a 2-of.

As for the sideboard, Ultimate Price and Feed the Clan are both good against Atarka Red. Duress is powerful against control and the aforementied Atarka Red, where it can strip the deck of the game winning combo.

I really hope you take this deck to FNM, I'd love to see how it turned out!

nateblego Corpseweft and Sultai Emissary are placeholders for Kalitas and Masterwork. Everything you suggested is good, but I don't know where to fit them. The list is kinda tight ATM, although I could see dropping Screeching Skaab for a combination of the removals. However, I want to keep my creature count up, and especially my Zombie count up. Torrent Elemental, although it is very good and has nice synergy, doesn't fit. I really wish I could run it, but there isn't really anything in the deck right now I can replace. You're on the right track with the sideboard; Atarka Red will probably be our worst matchup. I've actually been running an Assault Formation deck(based off of a deck I found on this site. I can link to it if you want it) at my recent FNMs. It performs okay, but it's so hilarious how it shuts down Atarka Red. I'm going to take a leaf out of that proverbial book and run 4 Disowned Ancestor, 2 Dragon's Eye Savants, and 2 Sultai Charm. Im kinda tired ATM so I won't start it right now, but I'll work on a sideboard and what to board in/out tomorrow for different matchups. Thank you for your continued support of my deck; you've helped a lot!

Love this deck, +1! I would replace a risen executioner for a Tasigur though, and I disagree with the sultan emissary. It's a very useful utility creature. If anything, I would run at least 3.

Disowned Ancestor is probably not as good as Sidisi's Faithful, because the Faithful can be a wall against Aggro and also can Unsummon a creature in a pinch. Yeah this deck is gonna have a hard time against Atarka Red, especially considering Bloodsoaked Champion can't even block. The sideboard should cover it though.