Erbium is one of the pricier elements of the rare earth group. The lanthanide series takes up a whole row on the periodic table and all are very similar chemically which makes their separation into pure metals a maddeningly difficult task. In erbium's case it also happens to fall on the rarer side which explains the price. A small sample of very pure (99.99%) erbium however is a pretty affordable entry for your collection of elements!
Five grams as shown, other sizes available also.