I'm new on Seabreeze, well be lurking a long time but not written much, so thought I would respond here to get a bit of practice!
Depending on where you live, its pretty easy to pick up an old small surfboard for around 200.00 to 250.00, or sometimes even for a 100.00. The guys that surf these sort of boards turn them over pretty regularly so there are heaps on the market.
You will need to use footstraps to start with, and so you need to glass in some footstrap inserts, so you have something to screw your straps in to. You can buy them online here
http://www.stubell.com.au/shopping-cart/board-building-components . The 5 HOLE FOOTSTRAP INSERT is best as it gives you some adjustment as you won't know exactly where to place them to start with.
You should also laminate some extra glass over the areas where you think your feet will be. If you can buy a board without too many depressions on the deck it will be easier to add a layer of glass or carbon fibre. The pressure on a board from kiting is way more than from surfing and has a longer duration, so you might get a sweet board and kit it up with straps and then wreck it in a season or two.
You need to buy pads as well as straps to make them a bit more comfortable and help the board last longer. You can find some on Ebay or probably your local kite shop should be able to help.
Hope that all helps!