The Eldrazi decks caused some significant price surges in the wake of the Modern Pro Tour. Chalice of the Void has more than doubled, for example. One of the biggest movers was actually a common, though it is a significant contributer to the degeneracy of the Eldrazi decks.

Spirit Guides were around $15 on TCGPlayer Sunday, and have now dropped into the sub-$10 range. This is a card that I would happily buylist off at this point, because I foresee it decreasing in price or at best holding steady in each of two possible universes.

The first is a universe in which Eldrazi is too good, and leads to bans. In this universe, demand for the card plummets due to its breakout deck no longer being a thing. Interestingly, Simian Spirit Guide itself could end up being the target for a ban. The card is only ever playable in decks that are trying to do something degenerate and more often than not in violation of Modern's turn four rule. There are some Ad Nauseum decks seeing success right now in addition to the Eldrazi takeover at the Modern PT, and frankly neither of these decks would be missed from the format.

Alternatively, the Eldrazi deck ends up being hated out of the limelight and is subject to no bans. Well, a deck being bad isn't much better than a deck being banned in terms of price movement. Prices are great right now, and I'd happily risk losing money in the long term by selling now and taking a sure thing.