upping 3 cards takes 4500

.
we have a round every week.
That means you just have to farm AI3 (worst case scenario) 4 hours a week.
I'm sure you can do that:)
If you can farm silver then it is even faster.
I have less upped water cards than you and only 7k electrum atm, but I'm making ~1k every day, even when I'm not really farm for money. If I do, I make 4-5k a day still without being serious. 10k+ if being serious.
(Additionally, simply being in the arena nets me another upped card every week, but that could change vastly depending on which league are you in)
the biggest problem with me is that every now and then I get wild and spend 30k+ on a random deck that pops into my mind

so I rarely have huge reserves.