Possible large surface cheap Köhler integrator?

Hi, I'd like to build an illumination system and I need a relatively large, evenly lit, surface. About a square having 50cm of side. I read online about Köhler integrator using fly eye lenses (aka lens array).
As the optical glass lens arrays are small, expensive and difficult to find, I was thinking about using the common Fresnel lens array films that can be found searching "multi lens film" on google. Those are usually used only for aesthetic purposes and they are not optimized for optical efficiency (even if the manufacturers usually claim over 90% efficiency).
What do you think about using them as a fly eye integrator system? They are very cheap and not difficult to find in large rolls, the biggest unknown that I can think of is the precision of the Fresnel lenses and their focal length, but this can be found easily with the help of the sun :)