Dual line kites vary in price. I like Prism kites. The stack ( 5 kite train ) is expensive. My Hyperkite is an antique, it was $150 back in the day, just for the kite. Another $40 for the lines ( 200 lb. test ) and I fly that with 150' of line. The Hyperkite has an 8' wing span and pulls like a mule. Prices for quality kites have come way down since then. I have a Prism Adrenaline with a 5' wing span that's lightning fast and not good for a beginner. A good starter kite would be around 6' wing span. Check around your area for any kite shops. This time of year they're getting rid of them for cheap. I'm partial to Prism kites because of the quality and they're setup ready to fly out of the box. Dual lines have bridles the lines attach to. If they're not right, the kite won't perform correctly. I'll be glad to teach anyone ( try to teach ) that wants to learn how to fly 'em.
Shayne