The engrams are sold in a four-pack — one each of green (uncommon), blue (rare), purple (legendary) and yellow (exotic) — for $19.99. They're squeezable stress balls made of polyurethane foam, measuring 3 inches high by 3 inches wide. They come packaged in a "clear plastic display box," according to the product page.
Bungie warned on Twitter that "supplies are very limited," so interested parties may want to snatch up the engrams as soon as possible.
Correction: Bungie had sold the engram toys before; this was a restock, not the first time the company offered them. We've edited the article to reflect this.