Thanks for your question!
If you apply online on our website for visa on arrival, the service fee for 1 month single tourist visa is $19US/person. Upon arrival, you must pay stamping fee in cash for Vietnam Government to get visa stamp and it is $25US/person
So the total cost for getting visa on arrival is $44US/person
Please go to this link to apply visa: https://www.vietnam-evisa.org/apply-visa.html