Though CA's laws are unjust, as well as annoying from a collector's standpoint, in terms of actually getting a decent firearm the laws don't hold you back that much. Which in itself brings up the whole pointlessness of the ban, but I digress.
For bargain-hunters, the SKS will set you back $150-200, and will do just about everything the AK will, and better in some cases (accuracy). Some variants of the SKS (those with detachable magazines or grenade launchers) aren't CA-legal, but the vast majority are.
Next up on the scale are the Mini-14, Mini-30, and Kel-Tec SU-16. Maybe around $450-ish if you shop around. I have not owned any of these products, but the overall opinion on THR seems to be patchy on the Mini-14 and -30, and gernerallly good on the Kel-Tec. The Kel-Tec seems to be a sort of AR-18 variant in a traditional-shaped stock which accepts full-capacity M16 magazines.
If you want to bump up to full-on battle rifles (military firearms in .308 or 30-06, and similar cartridges), the easy ones to get in CA are the M1 Garand ($350 through the Civilian Marksmanship Project
www.odcmp.com), or M1A, which is $1400 or so depending on variant.
There are also a variety of older military battle rifles, many of which _may_ be CA legal: Egyptian 8mm Hakim, French MAS 49-56, etc.
If it were me, I'd get the SKS if I wanted something handy and inexpensive, and the M1 Garand if I was willing to spend a bit more for something powerful. But if you have the cash for an M1A, don't let me stand in your way. Check out the "search" button on THR to read dozens upon dozens of past reviews of any of the abovementioned firearms.