Any of the B/x Zombie builds are pretty budget with B/R probably the most maintainable post Rotation(B/U loses Phantasmal Image, B/G loses Birthing Pod, B/W isn't really a thing). The money cards being Gravecrawler, Geralf's Messanger, and Falkenrath Aristocrat(If your B/R). Mono-black is also an option. I'd also look at Disciple of Bolas from M13 for inclusion in that deck.
Their may also be a B/R Vampires build between the Innistrad Vampires and Vampire Noctornus from M13.
The Mono-U Delver of Secrets/Invisible Stalker Runechanters Pike deck is one I've seen on Magic Online a bit and it looks pretty cheap to build being almost entirely Commons and Uncommons and probably gets the most from M13(Talrand and his Invocation). However it also relies somewhat heavily on Phyrexian Mana spells so I don't know how well it will survive rotation. But there are a lot of one mana Blue spells in Innistrad Block(Silent Departure probably being the biggest candidate).