To find out how many cans of tomatoes the food pantry still needs to buy, we start by subtracting the number of cans collected from the total number of cans needed:
\[ 1,021 , \text{cans} - 689 , \text{cans} = 332 , \text{cans} \]
Next, we calculate the cost of buying 332 cans at $0.95 per can:
\[ 332 , \text{cans} \times 0.95 , \text{dollars/can} = 315.4 , \text{dollars} \]
Since we need to find the approximate amount of money they will spend, we round $315.4 to the nearest hundred. Among the provided options, $300 is the closest.
Thus, the answer is:
\[ \boxed{300} \]