How much does a bitcoin investment cost?

Good afternoon, I'm curious about investing in Bitcoin and I'd like to understand the entry point. Could you please elaborate on the varying costs associated with a bitcoin investment? I've heard that the value fluctuates, so I'm wondering if there's a minimum investment amount or if I can start small and scale up gradually. Additionally, I'd like to know if there are any associated costs or fees that I should be aware of before making a purchase. Understanding the financial implications upfront is crucial for me to make an informed decision. Thank you for your time and assistance in clarifying this matter.