Sanctuary can be a good source of Eridium to buy backpack/bank/ammo upgrades at Crazy Earls. This particular 4 to 5 minute run yielded 7 Eridium but I have had numerous runs that have yielded double digit quantities. It is a fairly easy way to get 40 or 50 Eridium in 30 to 45 minutes to get more ammo to help get past spongy bosses or to create more storage space for weapons you want to keep.