How much is DeFi?

I'm curious, could you explain in layman's terms how much DeFi, or Decentralized Finance, actually costs? Is it a one-time fee, a recurring payment, or does it vary depending on the platform or service? And are there any hidden costs or fees that users should be aware of? Understanding the financial implications of participating in DeFi is crucial for those looking to get involved in this rapidly evolving space.