They will basically be like
this.
I will be selling the regulator, bracket, solenoid (without wall wart), needle valve, check valve and tubing. You will need to obtain the cylinder, 12V wall wart and diffusion method.
Cost to refill really depends on where you live. As low as a couple of bucks depending on cylinder size. These nano systems are not as cheap as a full sized system. But they are much smaller. And small will almost always cost more money.
If you are all truly interested then I will take $100 deposits on the systems. If there is not enough interest I will refund the deposits. Otherwise I when I get the 7 orders (by say the middle of next month) I will place the order and build and ship the systems.
PM for details if you need them.