I also would be okay with only buying all the Diablo items as a bundle, or only very specific transmogs for a larger individual price than in the bundle, if there is one transmog that I like.
For example, in the RoS Digital Deluxe Edition (upgrading it costs 20 Euros/Dollars for me) there is a transmog for Wizard Sources (The Heart of Darkness) which I find looks really amazing, however, since it is the only transmog of that whole bundle I like, I will not pay 20€ for that. For 2€ or 3€ I would might consider it (although that already is a bit high), but certainly not 20€.
There is another transmog that I find pretty amazing, also a Wizard Source (Guldan’s Secret), which was iirc a bonus for buying the 2014 Virtual Ticket, which I also would buy if the transmog would be available to purchase individually (I know it isn’t, but I would do it for the right price).