Here is a couple of our http://www.vietnamvisa-easy.com/blog/1-year-business-visa-campaign/advertisements for our business visas. We are one of the few VOA agencies that can arrange this. It can take from 3 days to process, but that costs extra. You might want to be more organised.
Pricing from USD420 for 6 months, or USD630 for 1-year business visas. We can also arrange for shorter 1 and 3-month visas link