It looks interesting but overbuilt for what it is. But even so, how are you getting to even $250 in materials? What type of wood, etc?
The only big expense is hardware for what you are doing
I see 12 pulleys, 2.50 - 3.50 apiece: $30-40 bucks (search for sheaves)
Maybe 8 casters for the desk to rid up and down on, may $30 bucks.
Steel cable or rope, $10-20 maybe.
Some screws, bolts, glue, varnish and wood. Maybe $150
And the design is cool but there would certainly be ways to do it cheaper, again looks really complicated and you really don't need the mechanical advantage of all of those pulleys being double like that. It will also still not be all that stable and difficult to get tight. If I were you and you really love the design, I would make the top part fixed to the legs and make the height adjustment part of the lower leg assemblies.
This is getting to look pretty complicated to get right, not from a woodworking standpoint, but from an engineering standpoint.