3 plans are there Consumption Premium Dedicated

• Consumption (Popular one)
  • You pay only for what you actually use (Pay as you go)
  • You pay for the 
    • Actual gigabytes you consumed
    • Actual function executions.
  • Draw back of this plan
    • Limit-  a limit of 1.5 gigabyte RAM. Means  your function cannot consume more than this amount of RAM. If you need more than that then go to one of the other hosting plans.
    • They do cold start 
• Premium
  • No Cold Starts
  • No memory limit (up to host ram)
  • Better performance
  • VNET integration
  • Predictable pricing 
• Dedicated 
  • Functions on an existing App service
  • if server under utilized.
  • because it uses a host that you are already paying for then there are no additional costs for the dedicated plan.