Hi Joe -- --
The most demanding for your application -- is the microwave. You will probably select a micro with the wattage in the range of 600-700 watts.
I'd recommend at the minimum -- an inverter rated at 1000 watts. Mine works just fine -- powering the micro and fridge at the same time along with the laptop. When the micro is at "full" I'm drawing 80 amps of DC current -- thats with everything on. So you see -- I've still got a safety margin.
I just looked at Flying J on the web -- they have a Statpower Portawatz 1700 watt unit for $ 149.00 -- although they are out of them at the moment on the Web. If you live close to one of these Truck Stops -- check it out.
Here's another Web Link listing inverters and pricing --
I don't know anything about the above link -- just did a search -- and I can't remember where I bought mine on the Web -- Senior Moment !! !!
Hope this Helps .....