TPS7A20 is 6.5uA, $0.10/ku. TPS7A05 is 1uA, $0.19/ku. It's not that hard to do better than 400uA!
And if you don't mind coughing up when it counts... TPS7A02 is 25nA, $0.45/ku. Triple the price, but more than four orders of magnitude better leakage.
If money is no object, there are some interesting chips out there. The LTC3335 chip[0] is a buck-boost that claims to have a 680nA Iq. Not as low as the TPS7A02, but it looks like it could make up for that in efficiency if your design does anything other than sleep.
And if you don't mind coughing up when it counts... TPS7A02 is 25nA, $0.45/ku. Triple the price, but more than four orders of magnitude better leakage.