Pricing – Seller Amp – Tools For Amazon Sellers – 22.95$ per month
Keepa – Amazon Price Tracker – 18$ per month
IP Alert – 100$ lifetime use
prepare-center.com – FBA prep center. 250$ one time fee for subscription.
Amazon’s Professional seller account costs $39.99 each month
So, initial investment would be 350$ (IP Alert + PrepCenter Pro version)
Monthly ~ 80$ + product costs.
Total expenses for first month – ~430$.
All mentioned above are good for newbie sellers up to the point you sell $2000 per month. Later you can move on to Online Arbitrage – Sourcing Software for Amazon FBA | Tactical Arbitrage, Dropship Automation Software | Automate Your Inventory & Orders (inventorysource.com), VAs and other stuff.