Hi,
That is a VERY low cost for a pure sine wave inverter. I am surprised to hear (from above post) that it is made by Xanterx and sold that low of a price. Sometimes the fine print is confusing, I have seen "Pure Square Wave" inverters, in a effort to fool the customer to thinking they are getting a quality unit, while they are not. Square wave inverters are just that, a square on-off wave form, just like the modified sine wave inverters are.
You might check customer reviews on that product.
There is also the saying "You get what you pay for" and you might not be getting a quality and energy efficient unit with that brand. But I might be surprised.
I would be looking at this website for a inverter.
SunElec.comFred.