.22lr rifle (ammo plentiful, cheap, buy in bulk, small game weapon, also deadly against bad guys if needed, could be most important gun in your collection)
Dependable rifle in .223/5.56 (popular NATO round, many guns shoot it, relatively cheap to buy ammo in bulk)
Dependable rifle in 7.62x39 (popular NATO round, many guns shoot it, cheap to buy ammo in bulk)