Since I asked the embassy and they got back to me, here is what it costs to go directly through the US embassy: From: Vietnam Consular [dcconsular@gmail.com] THE FOLLOWING FEE IS TOTAL FEE, COVERING FOR VISA STAMPING FEE, VISA APPROVAL ARRANGEMENT FEE AND PROCESSING FEE.
A. SINGLE ENTRY, ONE-MONTH: $100.00/
EACH
PERSON
B. SINGLE ENTRY, THREE-MONTH:
$140.00/
EACH PERSON C. MULTIPLE ENTRY ONE-MONTH:
$150.00/ EACH
PERSON D. MULTIPLE ENTRY THREE-MONTH:
$180.00/ EACH
PERSON
(their capitalization, not mine...
eek.)
travel.stackexchange.com/users/4500/Felix
From 29 August 2016, all visas will be issued in 1-year-visa multiple entry is granted for US citizens with maximum 90 days of stay per one entry to Vietnam.
The stamping fee at Vietnam airport for US citizens will be $135 USD you can read here:
http://tuoitrenews.vn/business/36900/vietnam-tourism-watchdog-decries-new-visa-fee-for-us-visitors tuoitrenews.vn is the reputable newspaper in Vietnam
travel.stackexchange.com/users/50984/chiro
Looks like a 45.00 USD stamping fee plus additional fees depending on how you process.
Additionally, you will need two passport photos and one blank page for the visa and one page with enough space for the entry and exit stamps.
In the past I have used this .
It may a seem a bit shady from a Western perspective, but it works.
travel.stackexchange.com/users/6541/Will
For stamping fee you have to pay at the airports1 or 3 month/single: US$ 45,1 month/multi: US$ 65,3 months/
multi: US$ 95
You need only 1 photo and your passport must been over 6 months valid.
For service fee, you have to pay to travel company to apply approval letter for you from US$ 10 to 20, it is depend on the company.
You have to pay for visa is service fee + stamping fee.
travel.stackexchange.com/users/19348/Tun Du Lịch
It depends on your nationality (some may not need), visa type,
how long you stay, normal processing or urgent processing...
As I researched, there are two kinds of tourist visa for 1 and 3 months and you can apply also for single entry or multiple entry.
Once arrived in Vietnam, tourists can also apply for Visa Extension of Tourist Visa if they want to spend more time here.
Stamping fee is the fee you pay the Immigration Officers directly and in cash (USD or VND) at your arrival airport in Vietnam (Immigration Desk/Counter) to have Visa stamped onto your passport.
The fee is collected by Immigration Officers and compulsory for all those who use Visa on Arrival method.
For 1 month single entry, stamping fee is $25/person For 1 month multiple entry, stamping fee is $50/person
The rate is displayed here ( Vietnam Visa Fee ).
Nowadays, it's easy to apply a Visa on Arrival online
(You will need to pay extra service fee, for $2 to $7).
travel.stackexchange.com/users/40713/J.Doe
The US Vietnamese embassy  website  lists the requirements for the visa application, but does not list the fee for doing so (though it does say  how  to pay it). The only information on the page about the fee is:   Fee for stamping visa can be checked at Consular Fee   What is the current fee for a tourist visa to Vietnam?
How much does a tourist visa for Vietnam cost?
travel.stackexchange.com
<visas><vietnam><tourist-visas>
travel.stackexchange.com/questions/25081
travel.stackexchange.com/users/4500/Felix
For 1 month single entry, the stamping fee is $25/person. For 1 month multiple entry, stamping fee is $50/person. There may also be additional  fees  depending on how you process it. For Vietnam, the visa stamping fee is 45.00 USD. 1 month single entry USD 25/person, 1 month multi-entry USD 50/person. 
For Vietnam, the visa stamping fee is 45.00 USD. 1 month single entry USD 25/person, 1 month multi-entry USD 50/person. 