|Google - http://finance.yourcentralvalley.com/inergize.kgpe/news/read/34217689/|
Purchased stamping fee $25 USD for single entry or $50 USD for several entry to get right back passport with visa.
For a VOA, you'll need a Visa on Arrival Pre-Approval Letter” from Vietnam's Immigration division, plus passport may be stamped at the point of entry. However if you'd like to stay much longer, or you desire multiple entries, you must submit an application for a visa. [ Link Details for Google ]