The kits themselves vary widely, OP pic was $150 whereas that last one was $10. Though, to be fair, that last one is 4 inches vs the first at a foot. As for supplies, I got most of them in a predone set for $10, but I've had to replace a couple things, for incredibly cheap though. Paint was like a dollar, and markers for lining the panels was about the same.
All you really need for this hobby is a pair of sidecutters (very small wire cutters), an xacto, and a fine-tip black or gray pen for panels. It's not too expensive really.