A couple of additional comments:
First, it is possible to re-use commercial cassettes, even with crimped tops, if you don't pry the tops off to unload them. Instead, unload them (onto your developing reel) via the film slit through which the film travels when it's in the camera. (You'll need to either leave a bit of leader protruding when you rewind the film or use a film leader retriever.) Cut the film at the end, leaving a centimeter or so protruding. You can then tape the bulk film to this film stub and re-use the cassette. Dead Link Removed has some embedded photos at the bottom showing the technique. You can even get cassettes from 1-hour labs to use in this way; most unload their cassettes as I described and are happy to give you their empties. This method of bulk loading has the advantage of being cheap and providing DX coding. (DX coded reusable cassettes are available, but AFAIK only in 100 and 400 speeds.) The drawback is that it involves extra trips through the cassette's felt trap, which increases the risk of scratches; and/or use of cassettes whose pedigree you don't know.
My second point is that it's possible to minimize the amount of fogged film at the end of a roll by attaching the film to the cassette's spool in a changing bag or darkroom. You can then use the bulk loader in the light, if you like, and unload it in darkness again. For the designs, like the Watson, with long exposed stretches between the film door and the place where the cartridge resides, this is the only way to go, IMHO; those long stretches result in two or three useless frames at the end of each roll if used in the light. If you use reusable cassettes, you can end up with no wasted frames due to fogging at the end of the roll in this way. When combined with the reused single-use cassette technique I just mentioned, though, it's hard to attach the film in the dark. Still, if you do the attachment close enough to the bulk loader's light trap, you can limit the fogging to a couple of centimeters. Depending on the semi-chance factors involved in loading the film into the camera, there's about a 50/50 chance of damaging part of the final frame, in my experience.