It depends how much you play and if your alliance or corp has an ore buy back program. With my corp buy back for ore I can mine a lot of ore with mackinaws and 5 retrievers. The most I mined was a week ago for around 4b isk. I try to average at least 2b a week. If you play a lot and don't have neuts bothering you then isk flows fast. If you are camped then you are screwed. What you make depends much on where you live. The alliance and corp you join determines how much you will make. Lucky for me my corp CEO is a boxer and has logistics to buy our ore. You may not be so lucky. In null the grav site rats will kill your miners. You need an overwatch to protect the fleet. I use a domi but would prefer something better. It gets the job done because my mack pilots have decent drone skills to help kill the rats.