Last August we spent 4 weeks away. 3 nights in Bangkok 25 nights in Laos (travelling from Huay Xai in north to island in South) + 1 night in Bangkok = 29 nights. In total we spent 3970 Euros (excluding flights BKK/Spain + insurance). This covered everything: all accommodation (cheap to mid-range), all transport (buses, boats, tuktuks etc), a couple of tours, food (mostly street markets or local restaurants), drinks, snacks, ATM commissions some cheap presents/clothes/souvenirs. That amount is for 4 people, including TWO double rooms per night. If anyone would like a breakdown of the prices, let me know and I’ll post it.
Thanks for the info, hopefully this will answer the many questions posted about cost of travelling.

Only helpful if you use euros. And dont tell me I can do the conversion. OP could have done that.

We are a family of 5 off to Laos (+ Vietnam and Cambodia) later this year. Your indication of costs is really useful. A breakdown would be great if you have the time.
Cheers
Here's a breakdown for food and accommodation:
Food (prices in Kip) (mostly street markets or local restaurants – all food vegetarian – meat dishes may be more?)
• Average breakfast: 18900 per person/meal
• Average lunch/dinner: 32460 per person/meal
• Average spent per day on snacks/fruit/drinks etc: 10750 per person
Accommodation (prices in Lao Kip) (ranges from cheap cabins to midrange hotels – mostly found when we arrived in each place)
• 1 night x guesthouse breakfast + takeaway lunch for four people (Pak Beng) 260000 (price for 2 rooms food)
• 3 nights x hotel: Villa Merry III Luang Prubang (prebooked before trip – can’t remember price)
• 2 nights x wooden cabins on riverside Phetdavanahn bungalows (Muang Ngoi) 40000 per room/night (cheapest on trip)
• 2 more nights: Villa Merry III Luang Prubang
• 2 nights Vayakorn guesthouse Vientiane 200000 per room/night
• 1 night guesthouse in Kung Lor (can’t remember price)
• 1 night x guesthouse in Tha Kaek 115000 per room/night (located where LP says Southida Guesthouse is, but didn’t fit description, is NOT clean or modern – do not recommend it!)
• 3 nights x hotel in Pakse 208000 per room/night (midrange: Sang Aroun hotel)
• 3 nights x hotel in Champasak 24,60$ US dollars per room/night (midrange: Inthira hotel – prebooked a couple of days earlier - offer found on internet Agoda.com)
• 3 nights x wooden cabins on riverside (Kham Pheng – Mr Tem, Don Khon island) 60000 per room/night
• 1 night x hotel in Pakse (Sang Aroun hotel) 220000 per room/night
Here’s a list of other bits I made a note of – it’s a bit long but will give you an idea of prices and the sort of things we spent money on. In Kip unless I say otherwise. Where possible I’ve put the price per person, but sometimes it’s more like a group price.
• boat across Mekong to Laos (Chiang Khong to Huay Xai) 40 BAHT per person
• border visas 6000 baht + 89 Euros (can’t remember why I have 2 prices here) – for 4 people
• tuk tuk to pier 3000 – for 4 people
• 2 day boat trip - Huay Xai to Luang Prubang 220000 per person
• beer in boat 10000
• laundry (LPB) 20000
• Palace (LPB) 30000 per person
• Phu Si (LPB) 20000 per person
• tuktuk to river 20000 – for 4 people
• minivan LPB to Nong Khiaw 80000 per person
• boat to Muang Ngoi 25000 per person
• hike to waterfalls with guide (Muang Ngoi) 110000 per person
• boat to Nong Khiaw 25000 per person
• boat to Luang Prubang 110000 per person
• bus LPB to Vientiane 160000 per person
• jumbo tuktuk 20000 per person
• bus tickets Vientiane to Kong Lo 150000 per person
• entrance to Kong Lor caves 2000 per person
• caves/boats 15000 per 2 people
• journey Kong Lo to Tha Kaek (3 stages): sawngthaew to Nan 25000 per person / next sawngthaew 25000 per person / final sawngthaew to Tha Kaek 30000 per person
• tuktuk to bus station 50000 – 4 people
• bus to Pakse 60000 per person
• tuktuk in Pakse (bus station to hotel) 40000 – 4 people (driver originally asked for double this!)
• a few extra bottles of insect repellent 181000
• daytour to Bolaven plateau 180000 – per person
• half day trip to Elephant village (price? – you can find this on internet – great fun for children)
• boat ticket to Champasak from Pakse 60000 per person
• tuktuk Champasak 20000
• bike hire 40000 – 4 people
• boat + bikes (Don Daeng) 180000 – 4 people
• bus tickets Champasak to Don Khon 70000 per person
• laundry 6000
• boats to island (Don Khon) 25000 per person
• boat to Don Khong hospital 200000 (total price for boat there and back – quite far)
• rabies injection in hospital 150000 (daughter was scratched by a cat, local doctor recommended jab)
• day pass (to visit waterfalls etc) 20000 per person
• boat trip to see dolphins across Cambodia border 100000 (boat) + 80000 (to cross border) – for 4 people
• boat to Don Khong from Don Khon 200000 – for 4 people
• bus tickets to Pakse 60000 per person
• tuktuk 20000 – 4 people
• 2nd rabies injection (Pakse) 145000
• bus tickets Pakse to Bangkok 235000