Apple Vacations is a large vacation travel package company, selling trips mostly from the east coast to the Caribbean. As I understand things, the same "guy" that owns Apple owns the USA3000 planes. A few years ago he started selling seats on their charter planes without the hotel package, hence USA3000.
We flew them once out of Baltimore and there were no problems, just great.
I was told by the agent then (a few years ago) that they start selling seats X-months before the flight (and I forgot the number), but found it not to matter. I happened to notice they started selling well before the date I was told and happened to look and bought quickly. The initial seats are reduced in price and go up as the seats sell. I find it hard to buy from them, but if you can get cheap seats, great.