Vietnam visas?

We are travelling to Ho Chi Minh City in April, staying with our son, who works there. We will be there just Thursday to Tuesday.
I realise we will need visas, but do we get them direct from the Vietnamese Embassy at £54 pp plus postage, or get the letter of approval and then get the passports stamped on arrival, which is cheaper? If the latter, does anyone know of a reputable company to use?
I realise we will need visas, but do we get them direct from the Vietnamese Embassy at £54 pp plus postage, or get the letter of approval and then get the passports stamped on arrival, which is cheaper? If the latter, does anyone know of a reputable company to use?