When the movie is half over, popcorn sells for half price. The full price of popcorn is $3.50, so the half price is:
\[ \text{Half price of popcorn} = \frac{3.50}{2} = 1.75 \]
Now, you want to purchase 3 orders of popcorn. The total cost for 3 orders of popcorn at the half price is:
\[ \text{Cost of popcorn} = 3 \times 1.75 = 5.25 \]
Next, the price of drinks is $1.35 each. For 3 drinks, the total cost is:
\[ \text{Cost of drinks} = 3 \times 1.35 = 4.05 \]
Now, we need to add the total cost of the popcorn and the drinks together:
\[ \text{Total cost} = \text{Cost of popcorn} + \text{Cost of drinks} = 5.25 + 4.05 = 9.30 \]
Thus, the total cost for purchasing 3 orders of popcorn and 3 drinks when the movie is half over is:
\[ \boxed{9.30} \]