The costs that hide outside the plan price
A VPS plan's headline price usually covers CPU, RAM, a disk and a bandwidth allowance. The bill grows with what sits around it: extra IPv4 addresses (now commonly $1 to $5 each a month, as IPv4 has run out), bandwidth over the allowance, block storage and snapshots, automated backups (often 20% of the plan price) and software licences such as cPanel, Plesk or Windows Server.
cPanel licences are priced by the number of accounts, and Windows Server and SQL Server are licensed per core, so a larger VM can cost more in licences than in hosting.