That is based on the rental rates after this change, which of course might change as you reduce supply of cards overall on the market. Plus on top of that remember that land will start to use up a ton of cards as well.

And the second point is you don't have to pay the 1 DEC per listing each day. You only pay it one time as long as your cards stay rented. So you might keep them rented for 3 to 5 days, which will cut that cost down as a % too.