If you would like to set up ceremony in a hotel in Vietnam. It costs around USD30++ per person. However, in the small hotel or restaurant, the cost will be cheaper. The cost might be around VND 100,000-300,000 per head + room charge around USD90-200 per night.
All of these not include wedding dress + make up or the money to pay for parent. It is only the cost of party during the wedding night. I see most of Vietnamese like to set up small party in front of their house, instead of setting up in the hotels.