Techniques for removing mains ripple
The low frequency of the ripple is the problem. Should the ripple frequency be 10kHz it's a lot more easily solved with components that are small.

I'd use an on-line switching power supply and forget about conventional transformers, bridge rectifiers and big capacitors. The output you get might have some higher frequency ripple and noise but this could be removed with low pass filtering from inductors and capacitors that are a fraction of the cost of filtering at 120Hz (full wave 60Hz).