Hi, what is the costs for 3 American citizens?
There is a Small Change for US Nationality (Effective Aug 25 2016)
Base on bilateral relationship between US and Vietnam, New policy for US nationality to apply visa to Vietnam from Aug 2016, Vietnam will issue visa valid for up to One Year Multiple Entry.
Tourist Purpose can multiple entry, but for each entry can stay in Vietnam up to 90 days only. The service visa fee is $35/pax and the stamping fee is $135/pax.
For Business Purpose, you also can multiple entry. However, you can stay up to 12 months. The service visa fee is $350/pax and the stamping fee is $135/pax.