Hi last time I went to Vietnam 2008 , my ticketing agent , in London , arranged Visa at reduced rate when I bought ticket , also they did not charge P&P which greatly add to charge .
Could it be that the charge quoted includes P&P , here in UK Vietnamese Embassy charge 8 GBP for postage for 1 return , just checked today .
Bangkok is a good place to obtain visas , most same day , through agents or in person , be prepared for long wait .