the cost to get a motorcycle license (class m1 or 2) at the CA dmv is $31.
you may as well get an M1 (good for any motorcycle / two-wheeled vehicle), as the testing / procedures is exactly the same as an M2 (good for mopeds only).
if you're over 21 you don't have to take the safety class, you can take the on-vehicle test as a substitute (i'd imagine it's easy as fuck with a moped). cost for the test is $6.
the fee to plate a moped in CA is $18, and you can do it entirely through the mail (even if you're not in-state!). it takes about 6 weeks for them to get the plate to you. this is a one-time fee you must pay to register each moped you have, or to transfer ownership for a bike you buy from someone else.
my insurance is $76 a year, progressive.