I use bulk loaded film and have done so for the last 30 odd years.
I get 18, 37 frame rolls of film + about 1/3 of a roll spare. There is a slight difference between 100' rolls and 30m rolls.
I load 37 frames to each roll to ensure I get 36 frames on my wide bodied Nikon F3's.
Basically you take the cost of a bulk roll and divide it by 18 to get your cost per film, it is that simple. You will also have a small roll of about 12/15 frames to use as a test roll, if you wish.
The best bulk loaders are ones where the film passes through a gate that opens up when closed, to allow the film to pass through untouched by anything.
Various methods are used by the different manufacturers to get the film through a light tight box in daylight to a film cassette. Some have a felt light trap, I'm not convinced that they are that good as eventually you may get some dirt or whatever entrapped in the felt, which may then leave a tram line running down the entire roll of film, not a great thing.
If you do a search on the site here you should find various threads on bulk loading and bulk loaders.
They really are a great way to save money, in this country. I currently have bulk loaded film that costs me $2.56 AUD per 36 frame roll to load. Purchasing the same film in a pre-packaged factory cassette, costs me about $8.00. That is a substantial difference.
Depending on the country you live in, bulk loading can be very cost efficient, or so so. Whatever, once you start bulk loading you will either keep on doing it, or give it the flick. Most people I know keep on doing it. The time it takes is minimal and you have the convenience of bulk loading 12 - 15 18 or whatever frames to a cassette if you so desire.
Mick.