Hi there, check out these 2 new products; Zacuto Z-finder can magnify into the LCD while the Hoodloup 3 can not. The Hoodloup3 is cheaper and should be ok to make it in any budget.
So it all comes down again into what you need and how much money you wonna spend.
There are by the way rumors that red rock is working on something similar aswell.
Here a video about the complete DSLR package called Gunstock Shooter from Zacuto:
here is a video of the cheaper Hoodloup3 solution: