What kind of necro build are we talking about? A Summoner aka Fishymancer (max Raise Skeleton, max Skeleton Mastery, max Corpse Explosion, using Amplify Damage to boost damage and break physical immunites and Decrepify to make Diablo and Baal a doddle) is very viable, and there is some good gear that is quite easy to come by/trade for. An example is the 'Lore' runeword (Ort + Sol in any 2 socket helm, circlet is the best bet). +1 All Skills, +30 Lightning Resist, Damage Reduced by 7, +2 Mana Per Kill, +10 Energy. Ridiculously cheap and easy to assmble, available at level 27, and still viable in Hell Act 5 if you don't manage to find anything else.