Just thinking off of the top of my head, I have a 12V system at my house which has been in place for quite a few years now, it is not my main power system, and only provides light for my laundry room and some seedling starting lights at the moment.
In thinking off of the top of my head about your proposal, I'm in at a bit more than $300, but a functional system might be something like this. you might be able to rig a 30 watt panel (I happened to see a 30 Watt Panel at Sunelectric Miami for $125 plus shipping but check all on-line vendors) A trace C12 charge controller or something similar with charge and integrated low voltage disconnect for $75 or less from EBAY, a marine deep cycle battery for about $80 (not very good, but you don't have enough current coming in at 30 watts for golf cart batteries which would be a step up and you budget precludes other, more expensive batteries), a small 12V 400 Watt inverter for $25 like one I saw at Amazon.com for those items for which you cannot get 12 volt auto style chargers for, and about 25 bucks for cigarette lighter sockets from an auto parts store and wiring, also I would probably pick up a 12V to 5V USB style cigarette plug adapter if I had devices that charged from USB. I don't like the durability of cigarette lighter sockets, so I would probably hard wire through switches the items which would not need to be mobile, In my case, I scalp old switches and stuff from old electronics. By the way, I have no affiliation with any of the vendors mentioned, they are just items that I have seen, and anyway, these are just some ideas.
This would give you a basic system with a 12V DC capacity to charge items from 12V, and a small 120VAC component for things that can charge from it, or in case of a power outage to run a small appliance or tool.
The next item to add would be more solar capacity as a fair percentage of what you would be making would be used up just keeping the larger 12V battery charged before you pull any power out to charge your smaller stuff. In fact, I would probably start with a second panel and two golf cart batteries myself. When you add up the cost of the power, you will find that the power from your small system will actually be more costly than the grid, but you will have the satisfaction of knowing that you made the power locally, and a bit of self reliance feels good. Rich
'A Joule saved is a Joule made'
