There are plenty of methods for earning money, and fighting the E4 is one of the most time consuming, least rewarding ones available.
I recommend you focus on making a PvE team for gym runs before making your PvP team. You'll be able to make around 250k per run, which may not sound like a lot but given how quick it is, it's a great way to make money. I would also recommend farming everstones. There isn't much of an investment needed like gym runs so this is great if you're low on money, usually makes me around 100k an hour.
If money isn't your issue I don't see why you would be farming the elite 4 to begin with. There are much faster ways to earn experience or as I mentioned money, so don't see the point of adding different difficulties to an already lackluster feature with little to offer.