Sorry, that was indeed nonspecific, you’re right. The add-on features for VPCs are commingled with the concept for me since they almost always go hand in hand. Internet gateways, transit gateways, EIPs, service endpoints, etc., and their fixed costs. Yuck.
All that stuff definitely adds up. I'm familiar with some low traffic projects with high "security" requirements that have so much overhead due to those sorts of adds-on. All the overhead winds up costing more than the actual compute + bandwidth running the site.