The D+ is a high end filter priced accordingly.
There was a nice rebate promotion over the summer, and you could buy the filers from AAP using their online discount codes.
Combine the two and you got four D+ oil filters for around $3.50 each including tax and postage after MIR.
Another possibility is to wait for an oil change special.
The lone K&N I've used, along with every M1 I've used were bought as a part of an oil change special.
Finally, some retailers may end up closing out these filters.
For example, Meijer has D+ and P1 filters on the shelf, but I doubt that sales will be all that great, so they will likely end up on clearance eventually.