Let us first solve the following subproblem: how many dollars must we pay to buy $G$ units of some ingredient?

This subproblem is easily solved by trying all possible numbers of large packages and calculating the number of small packages needed to achieve $G$ units. The solution is the smallest cost over all choices for the number of large packages.

Now we can check if we have enough ingredients for $S$ servings of the meal. For each ingredient, we know how many units we need for $S$ servings and we can calculate the cost for that many servings using the above algorithm. If we have enough money to buy all needed ingredients, then we can prepare $S$ servings.

A solution that increments $S$ while we can prepare $S$ servings will score $90\mathrm{\%}$ of points. To obtain the full score, use binary search to find the largest $S$ such that we can prepare $S$ servings.