Though your questions appear to be basic, they answers aren't simple -
1. All Garands are used. They were manufactured in WWII or the Korean War, so they are of that time period. Some may have been rebuilt to a very nice standard. In addition to reparkerizing, some may have a new barrel, new stock, etc. The internal parts may be checked to specification, or sometimes replaced with NOS parts (new, old stock) as available. From CMP, Garands run around $600 - $1000, depending on grade. Dean's Gun Restorations or Fulton Armory have rebuilt Garands for $1500 or so. (Springfield Armory, Inc. made a few reproduction Garands with cast receivers in recent times, but these are generally considered inferior to the forged USGI receivers.)
2. If you want a genuine piece of history, you don't want a Special Grade, which has a new barrel and new stock. However, there is nothing wrong with the Specials if you just want a shooter. If you go with CMP, they have excellent customer service and will "make it right" if anything is wrong with the rifle when you receive it. However, the exact condition of the rifle you receive will be somewhat subject to chance. Not all Service Grades are the same, in other words. DGR and Fulton Armory will have more predictable results, similar to a Special or better, at a higher price.
3. As all Garands were made to the same specifications, it is really up to the purists to argue over which manufacturer is better. Springfield Armory made most of them, as I understand things. Some manufacturers didn't make as many, and so they are "rare" by comparison.
I don't know California law, but I believe the non-detachable internal 8-rd magazine and lack of "evil features" makes the Garand OK to own in that state.