I think a "wall wart" is a very inexpensive way of getting power
for a PIC.  I've now got several products that use a 12V, 500mA unit
driving a 7805 regulator.  I think the wall warts are about $5 or less in
reasonable quantities.
        If you can put up with a nonisolated supply, consider the Maxim
MAX600, 601, 602, 610, 611, 612.  Info should be available at
http://www.maxim-ic.com  .

Harold