A cheap alternative is to make a wooden frame and mount a tracing paper on it using tape or stapler whichever you like. Clamp it in front of your light when shooting. Make sure it is at least 3 feet away for better diffusion. That's what I use in the studio sometimes if I am not using a softbox.
Either ways it will work. You just have to experiment and find out what you like. Of course there are other methods but I am not sure if I can conveniently share it here as these are considered trade secrets by pro photogs.