I haven't had the pleasure of seeing this tank yet in person but I have seen the pictures and have had discussions with a few people about it.
That being said, this is a revolutionary concept in making tanks/armor and may be the wave of the future. You know that King and Country and Honour Bound are thinking about this development. Although $300 may seem expensive, as Alex notes, you are getting a crew, and, most importantly, you are getting a tank that is very complicated to make with many different moving pieces, and much more complicated than has been made before. Since it is so complicated, it only makes sense that it will be more expensive than your normal tank.
Although not everybody can afford this, $300 is not an outlandish figure. Moreover, I doubt that, because of its complexity, it is yielding a very large profit margin for Figarti.