You want budget? How about an entire main deck that you can purchase for under $70? That's right, we're talking Manaless Dredge!
One of the most quirky decks around, Manaless Dredge enjoys the distinction of possibly being the least expensive existing archetypes in Legacy. This is due, in no small part, to the fact that it has literally no lands, or mana sources of any kind - no Lotus Petals, No Spirit Guides, nothing. Traditionally Manaless Dredge has been a pure combo deck, winning with a combo finish, but I've seen a second variation recently (linked below) which is more of a Zombie beatdown deck.
Manaless Dredge is high, high variance, and not for the faint of heart. When you lose, it can feel like you had no control over anything. When you win, though, you win in spectacular fashion. So how does it work?
Regardless of which variant you run, you're always going to want to start on the draw. If you've been playing Magic for a while, this can seem weird, since the vast majority of decks want you to be on the play. So you take your first draw step. Don't take any actions on your first turn, because you can't. Then discard down to seven cards. This is where the fun begins.
Optimally, you'll want to discard Phantasmagorian.
Then on your opponent's end step, discard cards to return the Phantasmagorian back to your hand. Optimally (again) you'll have a second Phantasmagorian to drop into the bin, and you'll be able to discard three again to mostly empty your hand.
Whether or not you have a Phantasmagorian to power up, you'll want to dump at least one dredger like our old pal Stinkweed Imp.
Once you have Balustrade Spy, Dread Return, and Bridge from Below in your graveyard, get the Spy onto the Battlefield with Dread Return, which will mill out your entire deck. Then use another Dread Return to get back one of your win cons. In this build, I'm running Thassa's Emissary for the combo finish.
There's another version, which I'll link to at the end of this post, which is more of a zombie beatdown deck, and doesn't rely on a combo kill.
In either case, Manaless Dredge has an Achilles' Heel. Graveyard hate.
Which brings us to the sideboard, which is where this deck gets expensive. You simply cannot win through an opening Leyline. RIP and Cage are also backbreaking. Prior to Modern Horizons, there was no answer to any of these cards. Now we have access to Force of Vigor, which can answer all of these.
Rest in Peace is still going to do some damage, because it exiles graveyards when it enters the battlefield, so you're going to have to try to rebuild. Leyline only exiles after it's on the battlefield, and Graffdigger's Cage doesn't exile the graveyard at all, so it's easy enough to get rolling after removing it. Force of Vigor is around $15, depending on the printing (some are cheaper), but it's the only answer to cards that absolutely kill your deck, so I consider it an essential component of the deck.
Other pricey sideboard options include Unmask for hand attack and, of course, Force of Will.
Well, thanks for taking the time to read all this! There's a ton more budget Legacy decks to talk about, so stay tuned.
Have fun, and be kind to one another.
Here's the more beat down version, with a great primer on playing the deck.