The Matter Reshaper only costs 3 mana to cost, but one of those must be a true "colorless" mana. In Eldrazi decks, this is really never going to be a problem. Best of all, when the Reshaper dies, he either puts a free permanent onto the battlefield or draws you a card. Either way, he can easily replace himself. Sure, if he gets exiled by a Path to Exile or Swords to Plowshares, you won't get the ability. But more often that not, you'll make sure that he dies. Keep in mind that he can also put a land into play, which is a nice gain in tempo.
Matter Reshaper was $6 in February 2016 at the height of his popularity. After dropping considerably in price, he was still $4 back in July & August 2016. But then, after basically disappearing from Standard play completely, his price cratered. However, in early March 2017 there was a mini price-spike to about $2.50, and after a slight dip afterwards back under $2, he's been on a slow, but steady rise again.
As part of a smaller set that was opened a lot, there are a lot of copies out there. But in a couple of years, with his consistent play in Modern, he could easily be a $4-5 card again. This is a card I definitely want a play-set of on-hand. Eldrazi is his best deck, and while you never know where else he may pop up, that's an archetype that's not going anywhere.