Ok, lets look at this;
Six cassettes w/coffins and loaded with 36 exp of film would be $120 plus shipping from Blue Moon.
I built a 'pull through' slitter (can also be docked between two 35mm cassettes to roll slit film into an empty cassette) for a total price of less than $20
It makes two clean, 9.2mm wide strips from 35mm film without scratching the film.
It is built with hobby plywood, 3 double edged razor blades, and a couple of 8/32 bolts.
I thought this thing out and drew up measurements before I started cutting the plywood.
Granted, I do have a small hobby drill press and tiny Proxxon table saw and there was some gluing and clamping involved.
Given that, it is a lot cheaper than this thing.