I've spent a lot of time the past couple of days trying to perfect a Modern Dredge deck. Something that I discovered is that a lot more people have access to hate than you might expect. In particular, literally any opponent could lead on turn one Grafdigger's Cage in sideboarded games.
While I was losing to the card playing Dredge, Cage has actually seen in increase in play as a way to combat Abzan Company as it hoses creatures entering the battlefield from libraries as well as from graveyards. What I'm getting at is that Grafdigger's Cage is becoming an increasingly popular sideboard card in Modern.
Cage has been slowly creeping up in price for a little while, and if Dredge becomes a deck that people play in paper tournaments and Abzan Company continues to put up results then I expect demand for Cage to increase.
I was actually expecting foils to be more expensive than they are due to relevance as a Vintage sideboard option, though currently the multiplier is only about 3x. I like Grafdigger's Cage as a position in foil and non-foil alike right now.