Hi Mad,
There are 29 travellers booked to travel to Vietnam. There are 13 travellers taking the main tour only with 16 of you staying on for the Cambodia add-on.
The unit of currency in Vietnam is the Dong. The US Dollar is the most favoured foreign currency. Major credit cards are only accepted in larger hotels, tourist restaurants and shops however, currency rather than credit cards is essential in remote areas, and you should ensure that you carry sufficient currency to cover your requirements. In Cambodia, the unit of currency is the Riel. We recommend that you take your spending money in US Dollars cash in small denomination as this is widely accepted.
I've taken the following from one of Bob Grays posts about his trip to Vietnam and Cambodia which will give you an idea of what he spent in 2013.
"I didn't bring any dong; some folks did but it was very easy to change it in the hotels. You can use $ in all the hotels, restaurants and shops - some will give change in $ and some in dong. The cost of drinks etc was a bit cheaper than in Europe - in some places wine was a little pricey, but no more than most restaurants or hotels at home charge: usually $3-4 a glass and often cheaper than this. Beer was cheaper at $2-3 a bottle. Fruit juices were delicious - I particularly loved the pineapple juice. I'd say I spent around $600 in total, including the Cambodia add-on. The same applies to Cambodia, you can get riel in hotels but there's no need really. There's around 30,000 dong to the £ and 4,000 riel to the £. Souvenirs such as silk scarves, pictures etc are very cheap and in most places you can haggle."
I hope this helps.
Kindest regards,
Julia
