Physical copies of that specific version are expensive. Streaming services usually host the "remastered" cut. Enter archive.org (The Internet Archive). It isn't just a library of old websites; it is one of the largest repositories of "out-of-print" media on the planet. You can find VHS rips, laser disc transfers, and—most importantly—the exact DVD rip of Fusion Reborn from 2006.
Don't let the "remastered" version steal your childhood nostalgia. Go dig through the Archive. dragon ball z fusion reborn internet archive
Unlike most DBZ movies (which follow the formula: Villain appears -> Goku struggles -> Gohan helps -> Spirit Bomb ), Fusion Reborn is experimental. The first half is a horror comedy set in Hell. The second half is a dimensional crisis featuring a reality-warping demon (Janemba) who fights with teleportation cubes. Physical copies of that specific version are expensive
And then there is .