Kodak sells 35mm in 400' rolls too. And short ends can come in odd sizes even smaller.
If you are making a 5 minute short film, a 10:1 shooting ratio means you need 50 minutes of stock anyway, so 4 or 5 1000' rolls would not be unusual. It's more a question of whether you want to run 5 minute loads or 10 minutes loads in your camera. You can buy twice as many 400' rolls if you wanted to instead of buying 1000' rolls. (1000' is 11 minutes at 4-perf.)
If you are making a 5 minute short film and think a 1000' roll is too much, you're basically thinking of shooting no more than a 2:1 ratio!
No matter how you slice it, a 4-perf 16mm format is not going to save you any money. You basically pay for real estate with film. And if rare camera format is generally hard to get deals on, not that such a camera exists.
Plus a 100' 16mm roll runs about 3 1/2 minutes, so a 4-perf 16mm format would barely give you a minute of run time with a 100' roll.
Certainly regular 16mm / Super-16 is cheaper than 35mm.