Amazon has the well-reviewed 250-count Halls Relief Honey Lemon Cough Drops on sale for $11 - 5% off with Subscribe & Save (can cancel anytime) = $10 with free shipping on $25+ or with Prime. Each drop contains 7.5mg of menthol.

The 180-count option is also on sale for $7.58 after S&S, but costs slightly more per drop.