The longer you kitesurf,
The cheaper it gets.

(If you so desire).
But in the beginning, it's expensive.
That's because you don't know much.
You might have the stoke, but you ain't got the savvy.(yet)
So ignorance makes for bad purchases.(But you can luck-out initially)
And experimentation costs dollars as well as valuable kitetime.
Think of it as money well spent on gaining information.
Resale value is the shopkeeper's empty promise.
Take what little money is offered for unwanted gear.
That will give you closure, you can now move on to the new stuff.
As you become more informed, the bargains magically appear.
I guess my point would be this:
If you kitesurf for say 5 years and the total cost was $15,000.....
(but $5,000 was spent in the first year alone)
then the annual cost over the long term was only $3,000. Only.
Nah, kitesurfing's not cheap.
Buy a boogie-board instead.