The black one's are Infinitesimal III's, also called 0.3's. The tops, bottoms, and trim are a black plastic called Persperex rather than the oak used on the 0.1's and 0.2's and the III's do not have a Watkins 5" woofer like the earlier two models but instead a conventional 5" poly cone speaker such as was used as a mid on other Infinity models. Consequently, $300 is pretty high.
The Infinitesimal's on sale are 0.1's and I'd also say that $350-$400 would be a fair price.