What it costs to start Amazon FBA
The seller account is the small part
An Amazon Professional selling account is a monthly fee. That fee is not the business. The business is the product you buy before anyone orders it.
Samples come before the batch
Order a sample and use it. Check the packaging, the instructions, and what breaks. A cheap sample that you never open is how a bad batch gets funded.
Inventory and freight are the real start
You pay the supplier, then you pay to move the goods to Amazon. Add Amazon prep and labeling if you are not doing that yourself. The amount that matters is the cash you cannot touch until those units sell.
Leave room for a failed test
Ads, returns, and storage can show up before the product proves itself. If the first test has to work or you cannot pay rent, the order is too big.