The basic mossberg 500 and remington 870 are pretty similar, in my book. I wouldn't have a problem getting either for what you're describing.

Unless you're planning to do a lot of hunting, I'm not sure you'd notice a significant difference between new and used. The nice thing about shotguns is that it's tough to really mess the barrel up, like can be done for a rifle. So new or used, changes of getting something that will work just great for what you're looking for are pretty good.

So I'd just see what I can get at what cost from the two guns above, and pick one up.

Sorry - not in Cali, I can't speak to what you'd have to do to get one there.