Either way in keeping with Canon's penchant for higher priced gear than the competition, there's little doubt the Canon challenge to the a7r/D800/D810, will be quite a bit more expensive.
I am not sure why you conclude that Canon is usually more expensive. My perception is different. Canon used to be both better and cheaper and only recently lost that lead.
Ok, let's look at what I use and it may give some idea of why I have the opinion that Canon gear is generally more expensive than nearest equivalent Nikon gear.
I currently own 1Dx, 5DMK III (The 1Dx was at release, much more expensive than the D4, the 5DMK III at release was much more expensive than the D800)
Currently list priced
1Dx $6799/D4 $5999/D4s $6499
5DMK III $3399/D800 $2999/D810 $3299
I currently own & use (among others) these Canon Lenses 200f/2, 300f/2.8 II, 200-400f/4, 600f/4 & I sold my 400f/2.8 II last year.
Current list prices
Canon 200f/2 $5999
Nikon 200f/2 $5999
Canon 300f/2.8II $6599
Nikon 300f/2.8 $5899
Canon 400f/2.8II $10499
Nikon 400f/2.8 $ 9549
Canon 200-400f/4 $11799 (Yes, it has a built in 1.4x)
Nikon 200-400f/4 II $6999 (1.4x costs $400 ??)
Nikon 600f/4 $10299
This "Trend" of Canon's being more expensive has been in place for a while now, I won't argue that the generally newer developed Canon Whites have an IQ advantage over the equivalent Nikon Lenses, but that argument doesn't wash with friends that use nikon, I prefer the Canon set up, and I've tried the Nikon set up (D800/D3x/D4).
What Canon "used to be" is to me less important than where Canon are today, they are more expensive, in the gear that I use, how they fit in the Market segments that I don't use is of zero importance to me.
In the area of FF Camera Bodies, and generally Long Lenses, Canon are more expensive, certainly more than Nikon & Sony, again, in many cases for good reason in particular over Sony, Sony have developed amazingly good Sensors & their Camera bodies are trending smaller, but usability, Lens line up etc is poor in comparison to Nikon/canon.