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.
The Idea being 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.
This one came out pretty nicely, I think. A fair, strait-shooting Midrange deck that fills starts out with Bounding Krasis, Grazing Whiptail and Assault Zeppelid to stabilize the board, and Boon Saytr if necessary, and then punches through with either Sagu Mauler, or by throwing the Saytr on any of the earlier creatures using Bestow, and you even get to turn creatures into frogs and play counterspells and all sort of fun toys.
As for the budget: Maindeck cost is currently at ~$10 (according to the middle blue numbers on this very site under estimated value), sideboard at about ~$2.50, nicely under my $15 budget.
So mostly this section is going to be notes on why I think these are good cards to learn from:
Bounding Krasis is a great 3-drop, since just a 3/3 flash for 3 would be playable, but it additionally can be used to tap opposing creatures to buy you time to turn the corner.
Boon Saytr is the secret mvp of the deck- a 4/2 flash for 3 is fine and powerful, but that in addition to the Bestow function that lets it boost up your other creatures to lethal levels makes it just a powerful card in all states of the game. Bestow might be pushing the complexity for these decks a touch, but not terribly, and besides Mauler's Morph ability, the deck is pretty straitforward.
Zeppelid is just kinda there, I wanted to make sure there was some flying in the deck, and Zeppelid can crash in for solid damage when it's called for. Untamed Kavu is a 5/5 vigilance Trample for 5, which is real good. It also has this silly mode where it comes in as a bear, which you won't use often, but sometime it'll save your bacon.
Oh yeah, Coiling Oracle is in this deck. It's good, it cantrips, occasionally ramps you a little, and gives you an early chump blocker on board.
The big beastie is Sagu Mauler, who's just big and mean and hexproof, so you just kinda get to run 'em over with it. Throw a Boon Saytr on him, and you've got some nasty guns headed in. The Morph ability might be relevant, but players can ignore it completely and still make perfectly good use of the card.
For spells- Essence Scatter is always solid, Illumination is your card advantage, easily cycled away if you can't afford it, Pounce is great in midrange, Negate is mostly for protecting your creatures, and Turn to Frog basically reads "Destroy target blocking or blocked creature.", which is pretty great. You can even use it to make Coiling Oracle trade with something, if you can't free up any blockers that will actually survive the fight.
Manabase is meant to be a touch lacking, but also super-budget. I'll be doing the same for all of them.
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.
Extra Mauler, the Naiad isn't Boon Saytr, but it'll do if you want more Bestow, and it's a decent 2/2 flier for 3 just as a creature, Mouth to Feed is fun in value matchups, though you can get blown out pretty hard with it, cancel, negate and pounce let you chose your own mix of answers, naturalize for hate, and sheltering word should be useful against agro, or if you want more protection for your creatures.