I kept notes of all my expenses during the Thailand portion of the trip and averaged out spending 1200 Thai Baht or NZ $48 per day, this includes the cost of my visas for China and Vietnam which were 2600 Baht each.
The average cost for some of the major daily items is below.
Accommodation 495 Baht/Day
Food 305 Baht/Day
Transport 70 Baht/Day
Entry Fees 45 Baht/Day
Accommodation: I stayed mainly in air conditioned rooms some of them quite nice. If you stay in fan cooled rooms or bargain better then I do you can probably do it for half this price.
Food: Three meals a day and plenty of coffee but no alcohol. I normally ate in restaurants but you can save yourself a lot of money by eating in the food markets. Any alcoholic drinks will add significantly to the cost.
Transport: This is largely intercity transport as I tend to walk a great deal when I am at my destination. Preferring an hours walk over a five minute taxi ride.
Entry Fees: Depends really on the speed with which you visit museums, temples don’t charge an entry fee but might ask for a donation.
Miscellaneous: I spend some money on Internet access, toiletries and a few post cards. The major expense were the two visas which I had arranged via a travel agent. You can get them a lot cheaper by going to the embassy and doing it yourself, but who wants to deal with embassy officials more than he has too?