Looks like I will be spending about 10 days in Laos and 5 days in Thailand. My budget for Thailand is £20 a day (1400 baht) and for Laos about £15 per day ($27). This includes all transport and accommodation and food apart from the two internal flights within Thailand I have already booked. This does not include the $30 Laos visa.
The currency in Laos is the Kip and the exchange rate is currently 20,000 kip to the British Pound or about 10,800 to the US dollar. I will take $300 into Laos and change some into Kip as required as the largest note is 5,000 kip. Most large expenses such as accommodation and transport can be paid for in US dollars. Food and drink will be Kip.
I may have overestimated the costs in Laos some people reckon on about $15 a day but best to have some in reserve.