An AP holder does not have to purchase a 1 day ticket anymore. Your reservation, however, is turned into a package to enable you to purchase dining. The package rules for payment apply ($200 deposit and paid in full 45 days before arrival).
The cost is the per day cost for the dining plan you chose times the number of people in your room. You have to get dining for each day of your room reservation.
We are planning to add the quick service dining to our April trip. Disney has had some funky things going on with the Codes associated with our discount, and "Harriett" has been working on applying the dining code to my AP discount room only reservation for over a week. (I've checked in a couple of times and they're working on it. Seems like it shouldn't take that long, but as long as I have my room only discount, I don't really care.)
We have a few TS ADRs, but we don't want to do TS for all nine nights of our stay and didn't choose any signatures this time. So, a QS dining plan will work well for us.
There are a couple of good threads on the
DDP forum explaining how to calculate the value. Spreadsheets and everything. I found those quite helpful.