So this is a project I wanted to engage in- To make a set of 10+ super-budget 60-card decks that are simple, relatively easy to play, relatively easy to understand, and bring across the fundamentals of how Magic Works. We've since gone way past 10, with tons more in the works, and I've really enjoyed the challenge of trying to make these decks easy to play and understand, fun, and all under a $15 budget, sideboard included.
The main goal here is that you could easily build these deck for a low cost and use them as an easy introduction to how magic works, to teach a group of new players both how to play, and give them a sense of Why, a sense of what fun things they're getting into. These decks aren't gonna be particularly good, or even legal in any particular format if it stops me from including a card I think is good for the deck, but they should be fun and interesting without being too hard to get into. They should be an easily-accessible example of how fun Magic: The Gathering can be.
Trying to add to my color variety, and to my agro options with Mono-B agro- a classic, a staple, a way to surely be the cause of your own demise. Greatness at Any Cost, right? Sadly, a lot of the best classics are too expensive for these decks, so we run Diregraf Ghoul, Tormented Hero, and Scalehide instead, but that's fine. We'll make do.
As for budget: Maindeck cost is currently at about ~$9 (according to the middle blue numbers on this very site under estimated value), sideboard at about ~$2, well within budget.
So mostly this section is going to be notes on why I think these are good cards to learn from:
Going up the curve- Gnarled Scalehide is classic black agro-2/1 for 1, no blocking. Straightforward and to the point. Diregraf Ghoul and Tormented Hero aren't quite as upfront, but get across the same point- big attack, no time for blocking, 'cause we gotta go face! Scalehide can also Bestow if you have nothing better to do. Sure, why not? Not why we're playing it, but why not?
Supported by those aggressive creatures is Mardu Skullhunter, which can make your opponents discard. Nice effect, has many benefits, good aggressive disruption on a 2/1 for 2, which is fine. Past that, Erg Raiders and Wanted Scoundrels are both overstated for 2 with some downsides you don't terribly care about, so go get 'em!
At 3, you have Herald of Torment. Ignore all that other text, this is a 3/3 flier for 3 that hurts you every turn. In other words- a really solid top-end to mono-black agro.
And, finally, Bone picker is a 3/2 flier for 1. Sure, it takes a little doing to make that happen, but kill something in combat, make a trade, cast Altar's Reap, I dunno, figure it out. Kill a thing and reap the benefits.
For spells- Altar's Reap I consider a Premier Black spell to learn with, and to understand the odd but gratifying patterns of play it leads to when used properly. Supernatural Stamina is sweet and lets you trade a creature off and then bring it back anyways, triggering Morbid effects like Bone Picker and our last contender- Tragic slip. Your creatures are going to die at times, that's just how this deck works. Often to your own Altar's Reap if to nothing else. Might as well capitalize on it, right?
Hey, it's mono-color, so I don't have to complain about the manabase, this is actually what you'd want from it. Neat.
As for the sideboard, this IS supposed to be a sideboard they learn how to use, to make their deck perform better in the right matchups, or just in general to customize their decks within constraints.
Mono--color sideboards are a pain in the butt, and mono-black sideboards are even worse, because you can't even hedge with artifact/enchantment removal.
What I manages is Typhoid Rats, as a blocker/trader/inconvenient-to-answer-attacker, if need be, a series of combat tricks to either kill bigger creatures, or just gain you life, extra Altar's Reap, and Pharika's Cure, which you can use as cheap removal and lifegain against other aggressive decks. You're already build to go fast against control/midrange.