If you have been paying attention to Modern at all, then you know that UW Eldrazi is the talk of the format. Because, you know, it's totally broken and is going to be banned. Aaron Forsythe has confirmed that an emergency ban won't be occurring, but you probably should have known that WotC isn't about emergency bans anyway. At any rate, the deck gets to exist for now, and because of it featuring four Adarkar Wastes the card has seen significant gains.

On the topic of things that you should already know, what I am advocating here is selling off of an Adarkar Wastes that you own. It shows up in Cubes and presumably Commander decks, though demand for this card outside of Modern is quite low. Upon the the Shadows Over Innistrad B&R list update you simply won't be able to sell this card for nearly as much as you can sell it for right now. If you need copies to play a Modern event, borrow them. If you own them, find a profitable way to stop owning them. In particular, if you own a copy in your Cube and/or Commander decks you are extremely likely to be able to sell them off and buy them back for less than you sold them for.