First, let's determine how much of the $3,000 will be spent on gasoline and motel rooms.
The family plans to spend \( \frac{3}{5} \) of $3,000 on gasoline and motel rooms. We calculate this as follows:
\[ \text{Amount for gasoline and motel rooms} = \frac{3}{5} \times 3000 = 1800 \]
Now, we need to find the remainder of the money after spending on gasoline and motel rooms. We subtract this amount from the total amount:
\[ \text{Remainder} = 3000 - 1800 = 1200 \]
Next, the family plans to spend \( \frac{1}{2} \) of this remainder on meals. We calculate this as follows:
\[ \text{Amount for meals} = \frac{1}{2} \times 1200 = 600 \]
Thus, Molly's family plans to spend \(\boxed{600}\) dollars on meals.