Christian buys 18 bottles of grapefruit juice at the corner store for a total cost of $15.66. If each bottle costs the same amount, how much is 3 bottles of juice?

Each bottle of juice costs $15.66 / 18 bottles = $<<15.66/18=0.87>>0.87/bottle.

Therefore, 3 bottles of juice cost $0.87/bottle x 3 bottles = $<<0.87*3=2.61>>2.61. Answer: \boxed{2.61}.