No, it was nothing like that. You choose delivery, area, magnitude and duration. You put multiples of these together. Nothing 'math problem', or spreadsheety about any of that. No more than enchanting, which is never, ever mentioned in the same breath as spreadsheety.

Formula for Magicka cost:
B = http://www.uesp.net/wiki/Oblivion:Spell_Effects / 10
M = Magnitude ^ 1.28
D = Duration
A = Area × 0.15
Total cost = B × M × D × A
1.4 - 0.012 × Skill
The Magicka cost is further multiplied by 1.5 if the spell is a targeted spell
The skill level requirement is determined from the base Magicka cost of the overall spell (summing the costs of all individual effects, and without adjusting based on your current skill level):
- Magicka < 26: no skill level requirement
- 26 ≤ Magicka < 63: requires skill of 25
- 63 ≤ Magicka < 150: requires skill of 50
- 150 ≤ Magicka < 400: requires skill of 75
- Magicka ≥ 400: requires skill of 100
A spreadsheet to calculate the cost is also available from http://www.uesp.net/wiki/User:Ong_elvin
They even have a link to a spreadsheet to use for Spellmaking: http://www.uesp.net/wiki/User:Ong_elvin
Source of information for all of these Spellmaking math formulas and spreadsheets: http://www.uesp.net/wiki/Oblivion:Spell_Making
So, you were saying?