First, we need to determine the half-price cost of the popcorn. The full price of popcorn is $3.50, so half price would be:
\[ \text{Half price popcorn} = \frac{3.50}{2} = 1.75 \]
Next, we will calculate the total cost for 3 orders of popcorn:
\[ \text{Cost for 3 orders of popcorn} = 3 \times 1.75 = 5.25 \]
Now, we will calculate the cost for 3 drinks. The price of each drink is $1.35, so the total cost for 3 drinks would be:
\[ \text{Cost for 3 drinks} = 3 \times 1.35 = 4.05 \]
Now, we need to add the total costs of the popcorn and drinks together:
\[ \text{Total cost} = 5.25 + 4.05 = 9.30 \]
Therefore, the total cost for purchasing 3 orders of popcorn and 3 drinks when the movie is half over is:
\[ \boxed{9.30} \]