Poison combo decks usually win with a low number of creatures. The list I'm thinking of runs 4 Phyrexian Crusader and 4 Phyrexian Vatmother and that's it. Plague Stinger might be ok to keep since it has evasion and Infect. The rest of the creatures either don't have infect so they require you to play cards like Phyresis, or if they do have infect they're just overcosted.

My sugesstions:

-2 Child of Night

-1 Drudge Skeletons

-2 Severed Legion

-1 Flesh-Eater Imp

-1 Hand of the Praetors

-1 Reaper of Sheoldred

-1 Ascendant Evincar

-2 Cremate

-1 Phyresis

-2 Decimator Web

-1 Bad Moon

-3 Unholy Strength (unless you keep Plague Stinger in, then +1)

-3 Terror

-1 Doom Blade

+4 Victim of Night (in mono-black it basically reads: 2: Destroy target creature)

+2 Lashwrithe

+4 Night's Whisper / Sign in Blood

+4 Phyrexian Vatmother

+4 Phyrexian Crusader (alternatively, since this seems like a budget build, stay with the Plague Stingers)

Funeral Cham has really good utiltiy in this deck.

Obviously more Inkmoth Nexus would be good, but also pricey.

I'd personally swap out the Tendrils of Corruption, Consume Spirit, and Corrupt for targeted discard. i.e. Thoughtseize, Inquisition of Kozilek, Wrench Mind, Raven's Crime, though the first two are a little more pricey.

With all of that discard Runechanter's Pike becomes really good. Just 1.

Disfigure, Dismember, and Smother are also really good removal.

Edit: How could I forget about Skittles? Skithiryx, the Blight Dragon could be a 2 of, but is about $7.