Cash Shop Specials: 7/31 - 8/07

Assuming these are the same prices as last time I think someone did the math and found out you actually spend less just buying the slots in sets of 8... I could be wrong though.

For Equip and Setup, it's cheaper to buy the MAX coupon so long as you have 44 slots or less, for Use and Etc, MAX is cheaper for 40 slots or less, for Storage, MAX is cheaper when you have 24 slots or less.

Compare the price per set of 4 slots (since you can really only add multiples of four to your inventory size, but I guess per slot would work too) given through both methods.

For Equip and Setup:
8 Slot - 6400 NX (3200 NX/4)
MAX - 41400 NX (41400/[(96-Current Slots)/4])

3200 > 41400/[96-Current Slots)/4]
3200 > 4 * 41400/(96 - Current Slots)
800 * 96 - 800 * Current Slots > 41400
(76800 - 41400)/800 > Current Slots
Current Slots < 44.25

For Use and Etc:
8 Slot - 6800 NX (3400 NX/4)
MAX - 46720 NX (46720/[(96-Current Slots)/4])

3400 > 46720/[96-Current Slots)/4]
3400 > 4 * 46720/(96 - Current Slots)
850 * 96 - 850 * Current Slots > 46720
(81600 - 46720)/850 > Current Slots
Current Slots < 41.04

For Storage:
8 Slot - 6400 NX (3200 NX/4)
MAX - 55800 NX (55800/[(96-Current Slots)/4])

3200 > 55800/[96-Current Slots)/4]
3200 > 4 * 55800/(96 - Current Slots)
800 * 96 - 800 * Current Slots > 55800
(76800 - 55800)/800 > Current Slots
Current Slots < 26.25

Max Inventory Slots is a bit more complicated, of course. We could divide the price by 4, and say that'd it'd cost 39760 NX to expand each inventory category to max. Then if we solve for current slots for 3200 NX and 3400 NX for sets of four, we'd get < 46.3 for 3200 NX (Equip, Setup), and <49.2 for 3400 NX (Use, Etc). So, I'd say MAX Inventory Slots is worth it if you have less than 88 slots combined in both Equip and Setup and less than 96 slots combined in both Use and Etc, but I'm not really sure that's right.