From the setting section, you can easily enable the taxes / fees option in the Modern Events Calendar plugin.
Over there you need to create the fee with your own specific criteria. Taxes and fees are actually they same in MEC settings. You just need to put a different name for each one.
Modern Events Calendar Taxes / Fees Options

Types of Fees in Modern Events Calendar
We have 4 types of fees in Modern Events Calendar:
Percentage
Apply a percentage per ticket.
Amount Per Ticket
It charges a fixed fee for your booking per each ticket.
Amount Per Date
It charges a fixed fee for your booking per each date.
Amount Per Booking
No matter what the ticket type is, this will be applied to the booking.
The above options are public and you can change the cost of tickets for a particular event too.
Disable Fees per Gateways
You can disable fees on your specific payment gateways with this option.
Taxes / Fees per Event
You can define separate taxes / fees per each event within the following path:
Single Event Edit Page > Booking > Fees
From there, you need to uncheck the “Inherit from global options” option and hit the “Add” button.
And here is how your fees will be applied to your tickets / events:
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