If you're quick, the 200gal box of reef crystals are on sale on Amazon and on Walmart's site. $37 or $39 per box which isn't bad!
Edit: I've never ordered from here but apparently chewy.com also has a similar price but you have to pay a little more for shipping.
Edit: I've never ordered from here but apparently chewy.com also has a similar price but you have to pay a little more for shipping.