for opening cases i'm currently at like +-0 profit.
i got 70% crap out of cases (5 times same tec9 in my inventory -_____- , a few ones to keep and 1 really nice p90 skin which i sold for 40€)
imo if you really want some skins for some weapons - buy them on the market place. for most weapons they are like maximum 0,50€. only ak,awp,m4 and special skins for pistols are really expensive.
you can check the live prizes for every weapon from every collection or random drop on this site btw:
http://csgostash.com/edit: still there are exceptions when it comes to gambling luck - friend got 2 knife skins already an awp,ak and m4 skin, but that is beyond normal luck a person can have imo. i'm just kinda lucky opening dota cases :c