an arf comes with everything. hardware, fuel tank, hinges, engine mount, even a spinner on many, this all adds up. In a kit your going to spend 30 bucks in glue and another 30-40 in covering material, minimum and with paint becoming harder to come by the the phasing out of lusterkote another 30-40 bucks in paint and fule proofing for it. So that 300 dollar ARF starts to look cheap as opposed to the 170 equivalent kit.

Plus the arf are built in china were wages are next to nothing and china can buy in huge bulk that even large company's here in the states couldn't touch, and allot of kits are actually cut here in the US with the cowls and canopys imported from over seas.
Also when you build your first kit your going to have to spend a tons in tools, People can bicker back and forth on what you really need in tools, but at least 300 dollars in tools is necessary to do it right. Things like a good building surface, pins, razor saw, hobby knife and blades, mini screw drivers, drill bits, dremel tool, hinging alignment tools, covering iron and heat gun, sanding t-bars, squars and rulers, pliers hemostates and a few others I'm missing that even well equipt mechanics don't have because they don't deal with small items required with planes.