Suggestions are encouraged/welcome!
I love mono black. It's my favorite deck style to build, and this deck is one reason why. You can sit back and blast your way to victory, and all with only 3 mana. The efficiency of this deck is ridiculous, you're always making plays, attacking, etc. There's rarely a dead moment, and if there is, you're probably not in a good position...
Also, since you don't have to pay for dual lands, it ends up being really pretty cheap.
Note: Adding cards like Mutavault is suggested. If you do, you should also run a copy of Urborg or two because this deck is heavy on Black symbols. The only reason they aren't on this list is because I wanted to keep it around 70$.
Why I picked what I picked.
1CMC
Bloodsoaked champion/gravecrawler: These seem pretty self explanatory to me. Pure damage. No one wants to waste a blocker on something that'll just get recast.
Diregraf Ghoul: this guy has pretty much no drawback; so what if you can't block on turn one? He's probably better than Isamaru, Hound of Konda because it's not a legendary creature.
Duress: Because why not run budget hand hate. It might win you the game if you throw out a Wrath.
Dismember*: this is pretty much a 1 CMC kill spell that can hit indestructibles, regens, and has no restriction as to what it can't hit. Pretty OP, if you ask me. Also, it's probably the best green removal in MTG.
2CMC
Nantuko Shade: woo... when I first saw this guy, I didn't think too much of him. Then someone told me to try it, and I liked it. A lot. This guy is the king of Combat tricks. He can kill something big, hit for a free two because your opponent is afraid to block, or can swing for 6-7 direct if they let him through. Also he only costs about a dollar. When you have him out, cast your creatures in Main phase two, you can trick your opponents. An alternative to this is Pack Rats.
Altar's Reap: Because draw is never bad. Sac a bloodsoaked champion, bring him back the next turn. Sac Geralf's messenger to pump and sting for two. Also it's instant speed, so it has that going over Sign in Blood.
Bile Blight/Victim of Night/Smother: I tried to pick a variety of kill spells that I felt would give me a lot of options. These are really down to preference, but these are a good starting point and are all pretty cheap. Other Options are Go for the Throat, Murderous Cut...
Tombstalker*: This guy can (and often is) cast for 2 mana. That's brutal. My other finisher, which I sometimes run, is Desecration Demon. Tombstalker is better with fewer lands, I find.
3CMC
Vampire Nighthawk: Obligatory black creature. Fantastic blocker, and can fly over stuff. Lifelink isn't bad either.
Geralf's Messenger: This is a really solid card. Sure, it enters tapped, but oh well it's basically guaranteed 4 damage+attacks
Gatekeeper of Malakir*: Yes, this is technically a 2 CMC card, but it's rarely cast for that because it's other ability is so powerful. He can hit hexproof, indestructible, really big guys, and any color. Really, really good.
Sword of Body and Mind: This thing can do some real damage in this deck. While it's not fire and ice, it's still pretty killer. The spawning of 2/2's is very nice, too. It's powerful but fair. Good card.
Loxodon Warhammer: I would run this even it didn't have lifelink. +3/+0 Lifelink, Trample is brutal. It can cause some huge life swings and usually guarantees a few damage being pushed through. Even if your creature dies you're gaining life and pushing through a few. Nice.
4CMC
Lashwrithe: A creature when you need it, a huge pump when you don't. Stick it on Vampire Nighthawk and you've got a 6/7 flying deathtouch lifelinker swinging on turn 4. Pretty solid.
That's it!
*not actual CMC