I used to back up everything on re-writeable DVDs. If the file was too big to fit on a DVD-5 disc (i.e., single-layer) I used DVD Rebuilder to shrink it to fit. I built an unRAID server several years ago when I got into Blu-Ray. I also bought a BD burner with about a dozen blank BD-R discs. I have yet to burn a single Blu-Ray disc with it. In fact, I've transferred all of my movies that I had backed up on DVD-RW discs to the server.
My server fits in a full tower case. My movie collection took up two shelves that were about 30 inches wide and ran floor to ceiling, and that's just for DVD movies. I've probably got another 450 movies ripped from Blu-Rays. You simply can't beat hard drive space for movie storage.
If you absolutely have to have movies on BD-R discs then Google is your friend. I used to buy blank media from several vendors. Taiyo Yuden was always considered to be one of the top brands for both CD-R and DVD-R discs, but I don't know if they offer BD-R blanks. I used to buy media in bulk quantities in lots of 100 along with the slim jewel cases and DVD cases. All I can say is, I hope you've got a lot of storage space for them because you'll be amazed at how quickly your collection will build.