William, whilst I might agree that the 1911 is on the expensive side we mustn't lose sight of the fact that FindMyPast have purchased this census as an enormous cost, plus, it is early, we have all been waiting for this census to arrive, we have a choice, 30 or 10 units, or not to purchase any at all and wait.
I reckon the reason why you have to buy new units is because of the huge layout FindMyPast have paid out to secure the 1911 before anyone else, old units from findmypast won't give them a new influx of money, perhaps when they are somewhere near having recouped the cost it will either be included in existing units or become a subscription, till then it looks as if we have to pay up if we want the information, we have the choice.
I am also on a fixed income and have chosen to pick and choose the units I purchase, on the whole it is a good thing for most of us genealogists
regards
Louisa Maud