theres actually a better way to save money.
just shell out $6 - 8 for a VOA invitation letter. this is not a visa but allows you to apply for VOA upon arrival in Vietnam. Check-in agent will be happy with this letter.
Obviously will cost more and is more inconvenient than e-visa if you actually go to Vietnam. but otherwise its a cheap insurance policy.
i did this for insurance when attempting to use my abtc card for a leisure trip in SGN.