This is quite difficult. The NASA wing is one of the least expensive kites on the market and can be made fairly easily from plans on the net. Essentially it is a single skinned kite without a frame and the bridle keeps it in a sort of triangular flying handkerchief type shape. It can be flown on 2 or 4 lines and apart from reasonably poor upwind performance it is a good solid workhorse. Foil kites (ram air kites) in the smaller sizes can be reasonably inexpensive. This type of kite has a lower and upper skin and air pressure keeps it inflated in an aerofoil or wing shape. Although they are available in sizes from 1 sqm to 10+sqm the smaller and hence cheaper sizes are not particularly useful since they need a huge wind to generate a strong pull. An interesting kite is the Peter Lynn C-Quad – another single skin kite but it has a basic “frame” made from carbon / fibre glass rod. This keeps it in a distinctive crescent shape. In terms of power per £ spent, the C-Quads cannot be beaten. They are however a bit tricky for beginners since they are so maneuverable and turn incredibly fast. Once you get used to them they are very powerful but I have seen beginners struggle to hold them steady and resist a sudden collapse. Overall they are not as user friendly as a foil kite but at the price well worth a look!!
There are other alternatives for example the “standard” 2 line Flexifoil power kites such as the 6 foot Stacker and 10 foot Super 10. At least with these you can start with one and build up an impressive stack which not only looks superb but also pulls well. Therefore the cost can be spread as kites are added. The main disadvantage is the relative complexity of launching and landing a stack of say three or more kites.