What you want to run is most important. Remember, you're converting 12 volts to 110, therefore, a 1,000 watt inverter will produce about 9 amps at 110 volts, but will require a 12 volt battery draw of 80+ amps. My alternator on my 25 gross HP tractor only puts out 20 amps, and the battery is a relatively small 450 cca battery. To run a 15 amp circular saw would require a 2000 wat inverter and you could only get a limited amount of usage on it. Even a 1,000 watt inverter would be tough on your battery and not give you much power.
A portable generator would not cost a whole lot more and give you 3,500 - 5,000 watts CONTINUOUS power and would be far more versatile.
If you just want to run some tools, once in a while, you can invest in an 18 amp RYOBI package for a few hundred dollars. An inverter will cost that much.