King of the cheap, ecological holiday - Beloved of backpackers. With WWOOFing you only pay for your own transportation to and from your destination (and your souvenirs). You do between 3 and 5 hours work a day on an Organic Farm (Participating countries all over the world). In return you get your bed and board and learn new skills. Host farms vary in size from simple smallholdings to full scale commercial farms. Work varies and can include babysitting, weeding, tractor driving, and animal husbandry (etc.). See WWOOF UK at: http://www.wwoof.org/wwoof_uk/ or go direct to the list of international sites at: http://www.wwoof.org/wwoof_uk/links.html
This is a worldwide organisation you can join (for free) where members can stay on peoples spair beds, couches, or floors, for free. Designed for backpackers, the networks has various safeguards in place such as verification of personal information and vouching by established members. Set up as an online network, one can choose where one stays (or who one allows to stay with you). This is a very cheap way to have a holiday. You don't get food, as you do wwoofing, but you don't have to work either, and the free couch is likely to be in the town rather than the countryside. Go here: http://www.couchsurfing.com/
Apparently caretaking can give one a cheap holiday (or a more permanent position). Basically, you housesit for someone, with arrangements varying from simply living in the house (and doing any necessary maintenance) to farming a farm for someone. There is more information at: https://www.caretaker.org, where you can subscribe to see caretaking opportunities as they become available.
For more normal, but cheap, holidays, it is worth signing up with Travelzoo. Every week they will send you the top twenty travel and holiday deals for worldwide holidays. Just as an example, this week they had found a deal for a four night stay in Cornwall for just £49 and they find some astonishing deals for exotic locations as well. Sign up at: http://uk.travelzoo.com/
Remember if you fly you can offset your carbon emissions to minimise damage to the environment. See the 'Ecoflying: What and How?!' page for more info: http://www.ecoknight.co.uk/ecoflyingwhathow.htm