We could get between $6k and $7k annually per citizen by swapping those plans for a basic income. If children don't count, we could bump that to maybe $10k. Obviously, this change would need to be taken gradually to not cause too much disruption.
To hit that $20k number, we'd need to increase taxes. Increasing consumption taxes would be fair. Since the flat credits is very progressive, it's OK to pay for it with a regressive sales or value-added tax.