Hi taxi4u,
The problem with PayPal should not be happening, Total is passed to PayPal along with Pick up and Drop off locations. Please provide us with temporary back end access and temporary server FTP log in via PRIVATE ticket so we can take a closer look.
For meet and greet at an airport you can create a Custom field Meet and Greet with a price of £6 and assign it to Airport group points of interest, add your airport points of interest to that group as well.
When a customer selects an airport from the drop down at the front end the Meet and Greet drop down will appear so the customer can select how many Meet and Greet packages he/she orders.
Here is the documentation of Custom fields:
http://kanev.com/docs/taxi-booking#h7-custom-fields
Alternatively, if you only charge once for Airport pick up you can add the price directly while creating the airport Point of Interest by adding Additional Charge Label eg. Parking (will be printed on user Order email and PDF receipt) and Price: 6 to charge £6 additional Pick up or Drop off fee.
Hope this helps.
Best regards.