For the marketing I don’t really see the issue. It’s very clear to me what the upfront cost is and this is a very common presentation.
For the Black Friday sale I’ve been able to apply it to an existing subscription as long as the new plan was longer than the current one. For instance I had an annual plan but during the sale I bought a two year plan. The rest of my first year got pro-rated to the new lower price. Didn’t expect that but it was my experience two years an ago.