Bundles of fresh herbs are on sale for $2.25 each. Lucia decides to stock up and buys 18 bundles. How much does Lucia pay for the herbs?

Lucia buys 18 bundles of herbs for $2.25 each, so she pays a total of 18 * $2.25 = $<<18*2.25=40.50>>40.50. Answer: \boxed{40.50}.