Hi Asemonick,
TESTing VALUES actually works really well on this question, but the values that you chose were problematic for a number of reasons:
1) With so many variables, you need 'variety' - ALL of your variables are multiples of 5 and two of them are DUPLICATES.
2) The number 100 tends to be great on 'percent' questions, but is not necessarily best for other types.
3) Smaller numbers tend to be easier to manipulate.
How long would it take you to work through this prompt if you used...
P = 3
C = 10
D = 2
S = 40... although ANY number ABOVE 30 would be fine (so that you actually have a profit).
I'll point out another couple of 'shortcuts' in the answer choices:
1) Notice how certain calculations show up more than once in the answer choices [for example, (p-d), (p)(c) and (d)(s) all appear in more than one answer, so you do NOT need to calculate them over and over - just calculate each one ONCE and then plug in the result wherever the 'term' appears).
2) Three of the answers end up NEGATIVE; as soon as you realize that that's the case, you can STOP working on that answer and eliminate it.
GMAT assassins aren't born, they're made,
Rich