Except for visa service fee, do I need to pay any fee at the airport? If yes, what is it

Besides Visa service fee, you will have to pay visa stamping fee by yourself at the airport. In order to get official visa stamped in your passport, you are required to pay stamping fee, you must pay it in cash (In Vietnam Dong (VND) or USD (US Dollars), so prepare it before your departure, they do not accepet credit card or cheque. Since 2013, the stamping fee is as following:

45 USD for single 1 month/3 month
95 USD for multiple entry