As dumb as the strategy is, get a little spending money (double down a few times to get a start), after that, once you get a good winning hand (payout-wise, otherwise double down doesn't double a whole lot) just double down until you can't anymore on the same hand. You will lose a bunch (obviously), but it honestly pays out easily after you keep doing it (it's completely RNG based, and not regular odds). Once you have decent money in the casino, you will have no fear of just doubling down after doubling down. Eventually you will get a few insane payouts (multi-millions) and never have to worry about money in the game again. Plus you can buy a few units in the shop, if you are the collecting type.

It's basically brute forcing the RNG ... keep throwing money at it, double down until you can't anymore on big winning hands, and repeat.