I agree with "AL-Bob" but would just like to point out that on top of this, it could also be a crazy hot US market playing some role. US collectors have a thing for high denominations & I have heard chatter on their forums that even circulated $1000 notes have been getting more & more dear. It could be that they're branching out to buy CDN $1000 out of frustration (thus driving up the price)? Not sure if the prices would be driven as high as 5 to 12K...but there could be an increase in demand for common $1000 notes. It would not surprise me.
American collectors influence the CDN collectible paper market more than most CDN collectors realize (or acknowledge). I believe they (& world collectors) help drive up Devil Face & now Modified banknote sale prices.
Speaking of "clueless," Banknote World started selling 100 Trillion notes from Zimbabwe in bundles & half bundles in 2016. I remember seeing these. This ugly note became the sweetheart of social media & the next thing we see is they're selling for $50 & more recently prices are nearly $100 for graded hyperinflation notes! Crazy!