Here is a price list in Laos for reference (by 2015):
A bottle of water (500ml): US$ 0.63
A local beer at a bar/restaurants: US$ 1.25
A glass of coca cola in a restaurant: US$ 1
Street food: US$3
Western decent meal at local restaurant: US$15
Laos more prefer its own currency Kip. ATMs in Laos dispense Kip. You may also contact your bank for detail instructions of daily withdrawals limit and charges. Credit and debit cards can be used in many shops, hotels and decent restaurants.
If you are going to bring cash to Laos, please take US dollar with you. Small notes will be very useful for tipping and local street shopping. Please make sure notes are in pristine condition with no defects, or they will likely be rejected as counterfeit. Get the most recently dated notes you can as these stand the highest chance of being accepted.
As to tour cost, you may compare