what dificulty are you playing? i played on both normal and hard and at the beginning i was just like you .. got up to 1100
but once you get to the middle with a bunch of lock picks/ do all optional quests/ go to every room and collect gold bars and coins from trash cans..you get to a poit where 3k is like the average ammount of cash you'd get..i'd pretty much splurge on primary weapons(machine gun and carbine) and my most important vigors (crow, the fire one and possession are priorities imo..)..planning to play it on 1999 mode sometime after i finish tomb raider ..people saying that mode will give you the work and get you shooked