I have taken a glance at some of those products and I think they are way overprcied. Sounds like a good chance for you to combine creativity with DIY skills. Plastic is hard to work with, what about using thin sheets of wood like chipboard?
Search for SCROG information in google, do your homework and sketch out possible designs so you can figure out what materials you will need to buy. I can't imagine that the whole project including electrics and lighting would cost more than $250.