Much less expensive? When they were in production.
But they aren't. So what's the point in comparing them? Very hard to find. And as has been touched on, the fact that d5k and d7k aren't in production makes 2nd hand ones more expensive than what they used to retail for anyway.
Also IMO the Fostex's look way nicer than the old Denons (and x99999 nicer than the new Denons).
The old Denon wood cups looked tacky IMO. Plasticky. The TH900 cups look much nicer/classier (though still shiny, be much nicer if matte) but still can't see myself wearing them. Guess I'm just not a fan of timber in HPs. Unless they are designed nicely, like these:
http://grainaudio.com/collections/grain-audio-products
If I knew they sounded decent I would've grabbed a pair of those OEHP on Kickstarter when they were on there but they might sound average.
Timber speakers on the other hand usually look much nicer but it all depends on the type of timber. Love that walnut they use on the Grain products