CHEAP inverters are the only way to go. I'm not familiar with the cobra brand, but i'm sure they're equal to other cheap inverters. I had a 2000/4000 peak coleman that was under 200 bucks. I currently use a pair of 775 watt inverters instead.
All of these "cheap" inverters create what's knows as dirty power. It's not the same power you have in an outlet inside your house. These inverters create what is officially known as a modified sin wave. Some devices won't work on this modified sin wave. Laser printers, some dvd players, transformers for X-10 camera's, are a few of the things i've found that won't work off of dirty power. Most devices are fine. Any incandescant light will work fine. Most devices that utilize transformers are ok (most devices that don't make heat or light use a transformer) Anything that makes heat will consume a lot of energy, and therefore be difficult to run with an inverter, but the heating element will work just fine with a modified sin wave. Most electric motors will also run just fine, but again can have a significant amperage draw.
The amperage of a 120 volt device needs to be multiplied by a factor of 10 to approximate the amps being drawn from the 12 v battery. For instance, if you have a frige that uses 120 volts, 7 amps. The batteries have to supply at least 70 amps of 12 volt current + the 10% or greater loss the inverter makes in the process of modifing the current. It takes a lot of 12 volt power to continously run any large device.
Tv's , computers, vcr, ect take very little power. My 25 inch tv takes approx 1 amp at 120 volts.
To answer you question......buy the 2000w inverter, you'll be happy with it. Just remember it's not magic, and if you're going to be using it without the bus engine running, you'll need a bank of batteries separate from the starting battery......Batteries are a whole new can of worms............
hope this helps more than it confuses.
Quis custodiet ipsos custodes (who will watch the watchmen?)