Switching power supply 220V-5V
Assuming you mean mA, not mAh, that's not much current. You can have a look at the chips by Power Integrations or Onsemi (NCP101x), for starters. Cheaper parts cost at the expense of more parts is achievable by using controllers without integrated switches (and external MOSFETs, of course). 



It's good that cost doesn't matter, because the transformer will not be cheap in small quantities.