Since Tesla is about to release a manual update that includes instructions NOT to use inverters with the car (I learned this the hard way... my car wouldn't start and had to be transported to Chicago for repair), I started looking for alternatives and found this for $240.
I just got mine, with a spare battery. It's very reasonably priced and it's completely amazing! It doesn't like inductive loads very much at high wattage (it balked a bit at a high-powered fan) but it's happy powering everything else. True sine-wave so it's just like wall power. It even powered up my 1966 Marshall JTM45 Super Tremolo amplifier and, at top volume with a Les Paul guitar, only sagged to 115VAC from 120VAC start point. It has enough power to light a 100W light bulb for an hour and twenty minutes, and only weighs 3.5 lbs. Battery swapping is instant. The batteries will charge off the charger or can be charged separately since they have an identical connector on them. I can't say enough about this thing. It's US made (components from various countries). My spare battery was $90. 260 watt hours (with the spare) of clean, buzz-free 120VAC power at 120Watts continuous and it sneaks right between the seats. I'm absolutely delighted!