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1,000 watts? Your entire alternator MIGHT supply 1,000 watts at full load for everything at once. Be careful you don't burn it out.
Watts don't change, whether input or output. So, if you have a 12v input from your cigarette lighter, and if your fuse on your cigarette lighter is rated for 10 amps, then that gives you a maximum capacity of 120 watts.
It's still a maximum of 120 watts at the other end, too. As volts goes up, amps goes down, and power remains constant.
I don't know who has the best deals, but rethink your requirements so that you get a realistic deal, wherever it's from.