There's not too much advice needed on gearing up a ranged attack-based Warlock.  With our starting gold, it'll largely be a question of Lesser Chasuble of Fell Power vs Warlock's Scepter, with maybe Gloves of Eldritch Admixture as a reasonably cheap way to add some extra energy damage when facing foes with regeneration or a special vulnerability.  Then something to boost stats and saves, and any extra gold can be spent on other potentially useful items.