Since 1st of January, 2013, Vietnam Immigration Department has changes stamping fee at Vietnam Airport for Visa on Arrival. Accordingly, one month single visa & three month single visa has the same stamping fee is $ 45 US; one month multiple visa (from 30 days) & three month multiple has same stamping fee is $ 95 US.
Please kindly note that stamping fee of ONE MONTH MULTIPLE VISAS may vary depending on your length of stay.
For example, if you apply for a period of 30 days staying in Vietnam, the stamping fee will be $ 95 US.
If you apply for a period of less than 30 days such as 29 days, the stamping fee will only be $ 65 US.
For more details, please kindly see Vietnam visa fee