API Key Management System

Hello, I am in need of a PHP developer who can create a secure API key management system that will allow users to sign-up for free api keys for various of our API endpoints/services with the ability to upgrade that api key to either a pay-as-you-go (prepaid) or a subscription model. Users should be able to fully manage their API keys (staff/admin is not necessary -- we are all comfortable with database management). The database must be created as well. Initially the payments should use PayPal but should follow a modular approach to allow other gateways in the future. Additionally, each API call is logged so usage statistics and raw logs should be available to the user. The database schema does not yet exist. This project may result in on-going improvements/feature enhancements. -- Please include the estimated timeframe in the bid.