Well... if you're happy with your deck as is, and feel comfortable enough that it CAN compete in the higher league, then there's a cheaper option:
Rent 100s of the cheap level-1 commons (even if it's a 100 of the SAME card).

These cards are all on the market for 0.1DEC and while they offer 0 benefit to your actual battles, they do boost your power and helps to unlock the next tier for substantially less than your 24K estimate ;-)