Many moons ago the People's Republic of Kalifornia had no access to AR15's and off list lowers. I did some research into an 80% completed receiver, and it comes with some pretty sweet perks. According to the ATF, if you build your own firearm for personal use (not to sell to others) it doesn't need a serial number or be registered. This option was quite expensive back in the day, and it required some technical know how mixed with a drill press. Truth be told, I'm far more gifted when it comes to being a smart ass and blogging writing than I am with tools. I gave up on this option when the first off list lowers came into the state.
With the onset of media based fear, and the fact it is pretty cool to roll your own lower, I'm curious to explore this option. Ares Armor is located in Oceanside, and they'll sell you an 80% complete anodized lower for about $90. They have build parties listed on their site and I've been told you can use their machinery all though I assume there might be a slight fee associated with that. If you want to DIY your lower at home a jig sells for $125.
Unfortunately, they are completely out of stock. I'm hoping their reserves will pick up soon, as this sounds like a pretty fun project. As always, I'm not lawyer (nor do I pretend to be one my epic blog) so do your own research.