Let's start by looking at what this deck loses by going super-budget-friendly:
Pack Rat: Yeah, it can take over a game by itself...well, itself and an ever-growing army of its closest cloned friends. There's no card replacing the kind of insane acceleration this little guy brings to the table, but there ARE plenty of cheap creatures we can roll out for 2 CMC (or less!) instead. Tormented Hero and Rakdos Cackler come down even sooner, and can apply a lot of early-game pressure. At 2 CMC, you've got additional pressure (and great black devotion support) with Rakdos Shred-Freak, and flexability with Thrill-Kill Assassin, who can unleash to make for another difficult-to-block threat or hang back to hold off the biggest counterattackers. So, no replacing Pack Rat, but you can use its slot (and then some) to make for a very aggressive attacking deck anyway.
Desecration Demon: Another big loss. Really not much replacing its offensive potential, but defensively, for the same CMC, you can sub in Deathgaze Cockatrice, which is even deadlier to swing into.
Nightveil Specter: I plugged a couple Mogis's Marauders into the same CMC slot, but obviously that's no substitute. To somewhat compensate for the lack of flying, I also plugged in a couple Gift of Orzhovas, but uh...yeah. Not much replacing this one...more adjusting the deck by it not being there.
Others: Thoughtseize is obviously awesome for nabbing creatures, but Duress can do everything else its much pricier cousin can, and without the life loss. Hero's Demise is as flexible as they come, but a combo of Ultimate Price, Doom Blade, and budget all-star Devour Flesh can somewhat compensate for the creature kill part, at least. (Planeswalkers are best Duressed or swung into with your deathtouched and/or hasty creatures.) Underworld Connections is ALMOST cheap enough to make the cut, but Read the Bones is a worthy enough substitute if you're really penny pinching.
With these losses, you may not take down any major tournaments with this sort of thing, but you should at least turn a few heads, and smaller tourneys and FNMs should be within reach. This has the potential to wrack up damage FAST.
So, enough about what we DON'T have...let's focus on the positive! With all those cheap creatures mentioned above, this can get in some serious lumps early on. Later threats like the Cockatrice and Marshmist Titan give it a little staying power, and we're still able to stabilize with good old budget-friendly Gray Merchant of Asphodel. He becomes a more critical wincon than your standard MBD, but he's quite well suited to the task.