Transit Gateway Pricing for various environments that I have

AWS Transit Gateway Charges you, here is the calculation for TGW Attachment for 5 VPCs as I assume that you would be having at least 5 attachments in that case.

Price per AWS Transit Gateway attachment ($)	$0.07
Price per GB of data processed ($)	$0.02

730 hours in a month x 0.05 USD = 36.50 USD (Transit Gateway attachment hourly cost)
1 GB per month x 0.02 USD = 0.02 USD (Transit Gateway data processing cost)
36.50 USD + 0.02 USD = 36.52 USD (Transit Gateway processing and monthly cost per attachment)
5 attachments x 36.52 USD = 182.60 USD (Total Transit Gateway per attachment usage and data processing cost)
Total Transit Gateway per attachment usage and data processing cost (monthly): 182.60 USD

Along with that you will be paying for the Data Processing as well with 0.03 USD/GB. Please note that the pricing may vary based on the AWS Region that you will select. References: https://aws.amazon.com/transit-gateway/pricing/