Amazon FBA costs do fluctuate, varying based on seasonality, the category and size of the items being stored and shipped, and various other factors. Here is an example of current Amazon FBA fees (as of 09/5/2019).
Monthly inventory storage (per cubic foot)
From $0.48 to $2.40 depending on season and size of item
Long-term storage (per cubic foot) – 181 to 365 days
$3.45
Long-term storage – Over 365 days
$6.90 per cubic foot or $0.50 per unit (whichever is greater)
FBA fulfillment fees (per unit) – Standard size
From $2.41 to $4.71+ (cost depends on weight)
FBA fulfillment fees (per unit) – Oversize
From $8.13 to $137.32+ (cost depends on size classification)
Inventory removal (per unit) – Return
From $0.50 to $0.60 depending on item size
Inventory removal (per unit) – Disposal
From $0.15 to $0.30 depending on item size