Is this a good price for a yellow cushion?

[pearaffair]

I've had my eye on this baby for a year or so.

Centre Diamond: 2.13ct Fancy Light Yellow Cushion Cut VS2, Natural & Untreated
Side Stones: 0.54cts Half Moon Cut GH/SI1
Setting: Platinum & 18kt Yellow Gold

$17,995.00 CAD

How can I tell if this is a good price or not?

I did some comparisons. I'll post below

 

[pearaffair]

$11,882 CAD
http://www.jamesallen.com/loose-diamonds/fancy-color/yellow/cushion-cut/2.02-carat-vs1-clarity-sku-628382

$20,000+ CAD
http://www.leibish.com/yellow-diamonds/fancy-yellow-cushion-18797

Granted, the Leibish stone is a Fancy Yellow, not a FLY, so I suppose that is greatly affecting price...

Also wondering about these grey areas on the side. Is this a form of bowtie?

 

[Sphene]

Many of the colored diamonds show gray areas I think it is the high hydrogen content which gives them their color that shows gray - yes I guess the bow tie effect - good cutting helps - this diamond not such a great cut by looks of it but the price compensates