I have no comment regarding your machine search, but I can share some of my thoughts on DVDs. I hope it helps.
DVD-R and DVD+R optical disks do still exist and can still be purchased online or in-store, though I believe the ISO size of Qubes OS (5.1 GB / 4.8 GiB) well exceeds the capacity of single-layer DVDs (4.7 GB / 4.38 GiB). Dual-layer DVDs (8.55 GB / 8.15 GiB) would be necessary for a DVD installation, which are harder to come by in stores. In my experience, DVD-R DL are impossible to find in stores and almost just as hard to find online; while DVD+R DL are not usually stocked in places like Wal-Mart, but can sometimes be found in large electronics stores and and always online.
It has been many years since I have used Windows, but I believe both recordable and rewritable disks can be reused “like a USB flash drive”, as Windows describes it, by running the disk as a “Live File System”. That is where much of this confusion probably comes from, and Windows does not help to dispel that. Whereas rewritable disks can be used in this way repeatedly, though, recordable disks cannot be “rewritten” so much as “written further”.
How recordable disks work is that they have a special dye coating them that is physically and irreversibly “burned” onto the disk in the binary pattern of whatever data you burn to it. When used “like a USB flash drive”, you are still burning the data to the disk, but you are not “mastering” it with that data, so any extra space left on the disk can still be used for future burnings. Once all the space is used up, however, there is not much more you can do about it. True to their purpose, they cannot be overwritten with further arbitrary data. (Technically, they can be forcibly overwritten with all 1s, which effectively wipes the disk, but this only works because you would be burning in every single bit rather than a binary pattern of 0s and 1s.)
So, while it is strictly true that recordable disks can be used as “write many devices”, it is only in a limited capacity otherwise consistent with how recordable disks work. To avoid this, you can choose instead to “master” the recordable disk. Make sure it is a DVD±R, though, if you want the benefits of a “write-once” disk. A more paranoid approach might be to force-burn the rest of the disk or otherwise fill it with random data before mastering. I think a Windows program called Nero has a “finalize” feature that more or less does that, though it is often used by people who dislike how “ugly” and “unprofessional” the burn line looks and want to push it to the edge. I have never used Nero and I am not aware of any Linux software with a comparable feature, though simply filling the DVD is sufficient.
If you want to be especially confident that you burn a legitimate copy of Qubes OS, be sure to verify the ISO checksum and PGP signature. It may also be best to do all this on a known safe device, one that has no history with malware or which at least has been successfully restored to a verifiably secure state. Once you have your newly burned DVD±R, you can then proceed to verify the checksum and/or the signature on other independent devices if you want to be extra confident. If they all report the same information, then either they are all lying to you or, more likely, none of them are.
Then, so long as everything checks out, you can proceed to install Qubes OS (or anything else) from a DVD with confidence.
More information about this can be found in the following Qubes documentation: